D&D 5E Basic Build Series: Cleric

Author: Esker

When many players think about Clerics, they think “healer.” In reality, while Clerics should generally have a few healing spells prepared, the primary role of an optimized Cleric is better thought of as a mix of buffing, area of effect damage, and a bit of battlefield control, while rocking a solid Armor Class. This build, part of the Basic Build Series, uses the Light Domain to layer instantaneous blasts (from the Radiance of the Dawn Channel Divinity ability and fireball spell) on top of the sustained “blasting” and battlefield control of spirit guardians to bring the wrath of their god down upon their enemies with unparalleled ferocity.

Race: Human (Variant)

Ability Score Increases – +1 Con, +1 Wis.
Feat – War Caster. As a full caster, maintaining concentration on your spells over the course of a fight is a significant part of your combat effectiveness. War Caster makes that job much easier.
Skill – Acrobatics. This option allows our Cleric to avoid and escape grapples more effectively, reducing the chances of being pinned down.
Languages – Common and Infernal. Sometimes you need to get inside the enemy’s head to defeat them. Or something. Well, we’re a fiery kind of Cleric, and the Hells are… Our choice of bonus language isn’t critical, and if you have any information about what languages you might encounter in your campaign then let that guide you. One consideration is that our command spell requires that the target understand us, so you may want to pick languages that enemies who don’t understand Common are likely to understand.

Class: Cleric

Skills – Insight, Religion. As a Wisdom based class, we’re well equipped to use Insight during social situations. Religion probably won’t come up that often, and even when it does we’re not going to be great at it since it relies on Intelligence, but as a Cleric people will likely expect us to be able to at least pretend we know something about it.
Divine Domain – Light Domain. We will be the best blaster in the game at low levels due to its powerful Radiance of the Dawn Channel Divinity that comes on at Level 2.
Bonus Cantrip (Light Domain feature) – We get the cantrip that shares a name with our Divine Domain for free, which is nice for us as a human without Darkvision.
Warding Flare (Light Domain feature) – Thrice daily we can impose disadvantage on one attack targeting us using our reaction. It’s a shame we have to use this preemptively rather than getting to see whether the attack would have hit, but it’s not competing with any other reactions, so we will definitely make use of it.
Spellcasting – Magic is a hell of a drug.

Bless – A d4 may not sound like much, but it’s roughly an increase of 12.5 percentage points in the success chance of attacks and saves. Proportionally, it’s an even higher increase: if, for example, a PC’s attacks would hit half the time normally, and you boost that to 62.5%, you’ve actually increased their output by 25%! 
Burning hands ^D – You have this one automatically from your domain. You probably don’t want to cast it, since a 15’ cone is unlikely to catch even three enemies, and anything that can be killed by 3d6 damage is probably something that will die to at-will attacks pretty quickly too.
Command – This can disable a creature (or two, if we decide to upcast it once we are able to) for a round, and potentially generate opportunity attacks from our melee allies in the process if we use the “flee” option.
Detect magic – This is just a good ritual that every party needs. If you have a Wizard in the party, they should grab the spell instead to open up a preparation for you.
Faerie fire ^D – Our other domain spell at 1st level. A decent buff to your allies, offering only one save to enemies in a 20’ cube, and giving everyone advantage against them if they fail the saving throw. It has some situational use for countering invisibility, but most of the time you’re likely better off using bless, which just works, no roll required.
Healing word – Use only in case of emergency, to pick someone back up from 0 hit points. Rarely do you want to use this preemptively, and never to “top people off”; it’s just not an efficient use of your spell slots.
Guidance – Add a d4 at will to anybody’s ability check. Use this whenever you can. If you know combat is coming, can safely make noise, and don’t want to pre-cast a leveled spell, cast this on yourself or another caster for an initiative boost.
Light – Comes free with our subclass. Good thing too, since we don’t have Darkvision.
Mending – Don’t heal people too often, but heal objects as much as you want.
Toll the dead – Your party should be focusing on one enemy at a time, so you should usually be able to use this on a monster who’s missing HP for the d12 version of the damage. Bong!

Ability Scores

10 Str, 14 Dex, 15+1 Con, 8 Int, 15+1 Wis, 8 Cha

We want high Wisdom for our spells, high Constitution for hit points and saving throws, and we want 14 Dexterity to take full advantage of wearing medium armor. That only leaves us enough points to bump one of our other scores to 10, leaving the others at 8. Having 10 Strength is nice when playing on a grid (the horizontal distance a character can jump with a running start is equal to their Strength score, so 10 feet gives us two squares, versus the one square you’d have with 8 Strength, which rounds down to 5 feet)) but it doesn’t matter much where we put the 10.

Background (Acolyte)

Skills – Perception, Stealth. Acolyte gives us Religion and Insight, but we already have those, so we swap them for two skills of our choice. Perception checks are both extremely common and important to every character. Stealth is another excellent skill to have, and will compensate somewhat for having disadvantage on the checks due to your armor.
Languages – Abyssal, Primordial. May as well really lean into the “know thine enemy” shtick. Maybe we were really into spooky occult stuff in high school, before we found the Light?
Feature – Shelter of the Faithful. Free healing for the party at temples or shrines? Don’t mind if I do. Pretty standard Cleric stuff.

Equipment

Cleric Starting Equipment

• A mace
• Scale mail
• A light crossbow and 20 bolts
• A shield
• Explorer’s pack / priest’s pack
• An amulet

Acolyte Starting Equipment

• A holy symbol
• A prayer book
• 5 sticks of incense
• Vestments
• A set of common clothes
• A pouch containing 15gp

Purchasing Goals

• Half plate armor
• Healer’s kit
• Potions of healing
• Bullseye lantern
• Spell components that have a gold cost (like diamonds!)

Level 1 Strategy

At this level, we’ll mostly be casting toll the dead or firing our crossbow. We should be aiming to commit either bless or faerie fire in a difficult fight, while saving at least one spell slot for healing word in case a teammate goes down. It’s usually prudent to pick yourself as one of the targets of bless because it helps you maintain concentration on itself, but the other targets (at least at this level) should probably be whoever does the most damage with attacks. Use Warding Flare if something scary is about to attack you.

Level 2 Cleric

Channel Divinity (1/short rest) – Like all Clerics, we can use our Channel Divinity to Turn Undead, forcing all Undead within 30’ who can see or hear us to make a Wisdom saving throw or have to use their action each turn for ten rounds to get as far away from us as possible. This most often takes things out of the fight completely, as long as your allies know not to do damage to turned enemies, which would snap them out of it, since your party can usually deal with everything else in the fight in a few rounds, and then focus fire any turned enemies that are still around one at a time. With every ally taking a readied action (triggering on the signal of whichever ally goes after the target in initiative, naturally) and a full turn, few things will survive long enough to act.
Radiance of the Dawn (Light Domain feature) – The reason to choose the Light Domain. If we’re not fighting Undead, we can instead use our Channel Divinity to do 2d10 plus our Cleric level to any creature of our choice within 30’ of us that fails a Constitution saving throw (taking half damage if they succeed). At this level this is an average of 13 damage on a failed save, which is comparable to the 2nd level spell shatter, but this is a much bigger area — bigger in fact than that of any area of effect damage spell below 6th level. Not only that, but it doesn’t even affect our allies. And we get it at Level 2! The average damage only goes up by 1 each time we gain a level, which is not great scaling, but it still does a lot of damage if we can catch enough enemies in it.
Harness Divine Power (Tasha’s Cauldron of Everything Optional feature) – We can exchange a use of our Channel Divinity for a spell slot of a level up to half our proficiency bonus (rounded up) as a bonus action once per long rest. It’s unlikely you’ll use this in combat yet because Radiance of the Dawn is more valuable than a spell slot in most situations at this level, but if you find yourself not having used your Channel Divinity at the start of a short rest, you may as well cash it in.
Spell Changes: +sanctuary.

Sanctuary – A bonus action casting time spell that forces any enemy that tries to target us with an attack or harmful spell to make a Wisdom save or redirect or lose the attack or spell. The main reason to prepare this spell now is to combine it with our Channel Divinity in the first round if we have to wade into dangerous territory to get into position for it to be effective.

Level 2 Strategy

The biggest change from Level 1 is that now we have Turn Undead and Radiance of the Dawn. Our decision flowchart for the first round of important fights is now, “Are we fighting undead? If so, turn them. If not, is there a large number of lower HP enemies within 60’ of each other and within 30’ of a space we can get to? If so, use Radiance of the Dawn. Otherwise, cast bless. If getting into position for Radiance of the Dawn would put you at great risk, you might consider casting sanctuary on yourself immediately afterwards with your bonus action to protect yourself. Since Channel Divinity isn’t a spell, it doesn’t prevent you from casting a leveled spell with your bonus action on the same turn. If something attacking you is likely to make its Wisdom save against sanctuary, you have Warding Flare too.

Level 3 Cleric

Spell Changes: +aid, +flaming sphere, +scorching ray.

Aid – Increases both maximum and current hit points of three friendly creatures (which can include ourselves) by 5 for 8 hours. You should be looking to rest cast this whenever you end the day with a 2nd level spell slot, and to use it in combat if multiple allies go down.
Flaming sphere ^D – We’re probably not going to use this but it’s a domain spell so we have it no matter what. Using our concentration to do 2d6 (save for half) fire damage to one creature per round with a bonus action, plus the threat of another 2d6 if an enemy ends their turn next to it is unlikely to be worth the spell slot or our concentration when we could be concentrating on bless (possibly upcast to affect four allies), upcasting command, or bringing up multiple downed allies with aid.
Scorching ray ^D – Our other domain spell at 2nd level. You might use this, if there’s a single dangerous target and doing somewhere around 10-15 damage to them stands a decent chance of denying them a turn they would otherwise get if we used a cantrip instead. But in most cases the spell slot is likely better spent elsewhere. Note that this may well do less damage than Radiance of the Dawn even if the latter only hit one creature, and it’s using a resource that we have less of.

Level 3 Strategy

Basically the same as level 2, except now we have a lot more spell slots, so we can be more liberal with bless, and can upcast it to affect four PCs, and we have a multitarget heal/buff spell in aid. 

You may notice a conspicuous absence from the spell list: spiritual weapon has been a staple of Cleric guides since 5E came out, so it’s worth saying a word about why it’s not here. We think it’s been overrated, and we highlight its shortcomings in our article on Overrated Damage Spells.

Level 4 Cleric

Ability Score Improvement (Feat) – Resilient (Con). We are one level away from getting our signature concentration spell in spirit guardians, so doubling up on concentration feats is well worth it. Plus it makes us better able to resist a bunch of nasty effects that involve other kinds of Constitution saves.
Spell Changes: +locate object, +sacred flame. 

Locate object – A useful thing to have available in dungeons, particularly if your DM treats “magic item” as a kind of object. Use it after you’ve cleared the parts of the dungeon that you know about to try to find areas and loot you might not know about. “Door” should be an uncontroversial use for helping find secret ones.
Sacred flame – As we go up in level, monsters tend to have better Wisdom saves, whereas their Dexterity saves tend to fall behind, so even though this does less damage on a failed save than toll the dead does in most cases, it can still be a better option sometimes.

Level 5 Cleric

Destroy Undead (CR ½) – If we use Channel Divinity: Turn Undead and any CR ½ or lower undead fail the save, they are instantly destroyed instead of being turned. Usually not a big difference in the end, but saves some cleanup.
Spell Changes: +daylight, +fireball, +revivify, +spirit guardians, -sanctuary.

Daylight ^D – A domain spell which is basically a really expensive light spell with a big area. If this produced actual sunlight it would have some use against certain enemies, but no, we have to wait for 5th level spells for that.
Fireball ^D – Traditionally the purview of arcane casters, we get this as a domain spell. This may not do as much damage as spirit guardians in the long run, but immediate damage is better than equivalent damage spread out over time. Plus, it doesn’t use concentration, and can be cast from range. Don’t assume that round 1 is always for your concentration spell; in a situation worth spending a 3rd level spell slot where fireball is good, there’s no reason not to lead with it.
Revivify – Parties shouldn’t expect Clerics to cast a lot of healing spells, but expecting them to have this spell prepped once it’s available is legitimate.
Spirit guardians – This spell is as integral to playing a Cleric as eldritch blast is to playing a Warlock. It may as well be a class feature. If you’re going to be in melee range and enemies are too spread out for fireball, are approaching in waves, or it looks like it’s going to be a long fight, this is probably the better bet. It not only damages them when they come within 15’ of you, it also slows them down (not to mention damaging them again when they start their next turn). Many DMs treat the area of the spell as equivalent to difficult terrain, but as written, enemies who enter the area have their speed halved, which means that if they’ve already spent half their original speed to get there, they are stopped in their tracks, which is better than difficult terrain. On the flip side, if an enemy starts 5’ from you and spends 15’ of movement to leave the area, their speed is restored to normal, having spent only 15’ (not 30’ as if they had been walking through difficult terrain). So when the effect of spirit guardians functions as written (versus difficult terrain), it’s harder for enemies to get to you, but easier for them to leave.

Level 5 Strategy

You have two shiny new big weapons in fireball and spirit guardians, and you should use them if they will help your side win the fight with fewer overall resources spent (which includes hit points). But also don’t be afraid to just cast bless if it’s a fight your side can win with minimal cost, and don’t ignore Radiance of the Dawn. It may be less damage than a fireball, but you get it back on a short rest (though now that your proficiency bonus is +3, an unspent Channel Divinity can be used to recover a Level 2 spell slot now, albeit only once per long rest). Your basic flowchart still starts with Turn Undead if it applies. If not, and there are a number of potential targets, you’ll need to decide whether to lead with Radiance of the Dawn, fireball, spirit guardians or just something like bless, with an eye toward maximizing the potential impact on how cheaply your party can win the fight, factoring in the resource cost of whatever you do. When using spirit guardians and wading into melee range of enemies, don’t be afraid to spend your actions Dodging. The incoming damage that prevents is often worth more than doing a little bit of cantrip damage.

Level 6 Cleric

Improved Flare (Light Domain feature) – Now you can used Warding Flare to protect an ally! We should have no problem expending all of our uses for this each day.
Channel Divinity (2/short rest) – Twice as many uses for either Turn Undead, Radiance of the Dawn, or using it with Harness Divine Power to regain a spell slot of up to 2nd level. You can now use Harness Divine Power twice per day, which means you can have up to 5 2nd level spell slots.
Spell Changes: +dispel magic.

Dispel magic – Somebody in the party should have this on hand, but you probably don’t need more than one person. You’re a pretty good candidate to be that person due to the large number of spells Clerics can have prepared at once; on the other hand, Bards and Sorcerers get boosts to any ability checks they have to make with it. Coordinate with your party if multiple people are capable of taking it.

Level 7 Cleric

Spell Changes: +divination, +guardian of faith, +wall of fire.

Divination – This can be used to get useful information about something your party plans to do. It’s a ritual, so it doesn’t use a spell slot, but it does have a material component with a gold cost which is consumed, so stock up on that incense. The DM gives you a truthful reply to your question, but expect table variation in how interpretable or cryptic the responses will be.
Guardian of faith ^D – A domain spell for the Light Domain. It’s written like it’s meant to be a camp spell, given the 8 hour duration, but it can actually be useful as a combat spell, particularly if your party has forced movement effects to trigger the damage, or there’s a choke point enemies have to move through. However, you only have one 4th level slot now, and you almost certainly don’t want to use it on this. At higher levels though, when 4th level slots are not as big a resource, you might use this sometimes.
Wall of fire ^D – Our other new domain spell. Not bad if your party can push enemies through it forcing them to take the damage again, or even two more times if they want to get back to you. Notice that after the initial damage to creatures in the wall of fire’s space when it appears, subsequent instances of damage offer no saving throw. So even though on the surface the 5d8 looks like not much more damage than spirit guardians upcast to 4th level, because it has no save it’s actually something like 50% more per triggering instance. That said, it’s harder to get enemies to take damage from it without particular kinds of movement assists from your allies. So upcasting spirit guardians is likely still the best use of this spell slot in most groups.

Level 7 Strategy

Most days you probably just want to use your 4th level slot to upcast spirit guardians, but in the right situation, a wall of fire may be preferable, particularly if you want to block line of sight. If you have the slot left over at the end of the day, use it to rest cast aid.

Level 8 Cleric

Ability Score Improvement (Feat) – Telekinetic (+1 Wis). This half-feat from Tasha’s Cauldron of Everything gives you an enhanced version of the mage hand cantrip, but more importantly it also lets you move a creature who is willing or who fails a Strength save 5’ toward or away from you. This can be useful to get an ally out of a hazard or a grapple, but the big thing we want from this is the ability to pull enemies into our spell hazards, especially spirit guardians. If we force them to enter the spell’s area on our turn, they take the damage then, and then again when they start their turn. There is no size restriction, although bigger creatures will tend to have better Strength saves. Note that the two effects of this feat do not depend on each other at all; you don’t need to have an active mage hand to use the forced movement.
Destroy Undead (CR 1) – Now ghouls and specters are instantly destroyed rather than sent running when you use Turn Undead.
Potent Spellcasting (Light Domain feature) – A slight damage boost when you aren’t using the Dodge action (which you will still be doing often).
Spell Changes: +stone shape, +mage hand. 

Stone shape – Being able to tunnel through a wall, create cover, or seal a room can be very powerful in dungeons. If you know you won’t be in a stone environment on a particular day, you might want to use this prep slot for a lower level utility or situational spell, such as clairvoyance or remove curse.
Mage hand – You get an enhanced version of this cantrip via the Telekinetic feat, letting you cast it without verbal or somatic components and making it invisible. Which could come in handy if you want to steal something from a table while you’re in the middle of a conversation.

Level 8 Strategy

The big change to your tactics at this level is that you want to be using Telekinetic shoves with your bonus action on basically every round. If an ally is in a dangerous spot such as a grapple, pull them free. If you need to clear the way for a fireball, push the ally out of your perfect area you spotted for it. If your unlucky melee ally just needs 5 more feet to close into melee next turn, give them a boost. Otherwise, when you cast spirit guardians and every turn while you have it up, position yourself so that an enemy is just outside its area of effect, and try to Telekinetically pull them in so they take damage on your turn and then again on theirs. If they make their Strength save, then just move so they start their turn in the area. You can also use this trick to squeeze extra damage from guardian of faith or wall of fire.

If you ignored our suggestion at level 3 and have been using spiritual weapon since, now you definitely want to swap it out. Telekinetic provides you a very premium bonus action that you can spam without spending resources. Used only for the extra damage benefit, Telekinetic shove into your spirit guardians should easily outpace what damage you could do with spiritual weapon.

Let’s clarify why this works so effectively. First, here is the relevant excerpt from spirit guardians:

Note the use of turn instead of round, and the use of the word enters. Keep an eye out for other spells with this wording, once you start looking for it, you will see it everywhere.

A creature can absolutely be subjected to the damage of spirit guardians multiple times in a round, it is limited only by turns. The only way a creature “normally” can enter the area is with movement on its turn. However, according to the Rules as Written clarified in Sage Advice, forced movement is intended to trigger spells like spirit guardians that require a creature to enter their area of effect! Here is the relevant excerpt:

Level 9 Cleric

Spell Changes: +commune, +flame strike, +scrying, +banishment, -detect magic.

Commune – A ritual that lets you ask your deity three yes or no questions and get correct answers for each one, unless the DM decides the questions are beyond your deity’s knowledge. This complements divination, which only gives you one question but can be an open-ended one. This spell has no costly material component though, so you may as well opt for it over divination if either one would do what you want. Like divination, the DM has an “out” if they don’t want to answer your question, this time in the form of saying your deity doesn’t know (as opposed to giving a cryptic response). Of course, if you use divination first and get a cryptic response, you could always use this afterwards to clarify its meaning.
Flame strike ^D – Just a terrible spell. A smaller area and less damage than an upcast fireball, and fireball does not scale well. The only small situational advantage this has is that half of the damage is radiant, but the other half is still fire, so if enemies are going to resist or be immune to fire it’s still bad damage. Unfortunately we’re stuck with it as a domain spell.
Scrying ^D – This has some nice utility if you can use it to spy on an important NPC or enemy. Major bosses at this level, let alone the BBEG, will likely have legendary resistance, but you still might be able to spy on them if you target an area or one of their associates rather than targeting them directly. Note the material component with a gold cost.
Banishment – Remove a creature from the fight if they fail a Charisma save. They come back after the spell ends unless they’re native to another plane, but as long as you can maintain concentration until the rest of the enemies are dealt with, it’s usually pretty easy to finish them off by dropping concentration right after their turn so you everybody gets both a readied action and a turn before they can act. You might not want to cast this very often with a 4th level slot, because if the target makes the save then youI did nothing on your first turn, but upcasting to 5th to target two enemies increases the chances that at least one goes away. If you’re lucky you might get both.

Level 9 Strategy

Spirit guardians remains your staple concentration spell, and upcasting it is often going to be the best use of your 4th level slots. If you have a tough fight against a small number of enemies who are powerful but don’t have Legendary Resistance, you may want to use your 5th level slot on an upcast banishment. As you are able to use 4th and 5th level slots for your big concentration spells more often, you can be a bit more liberal with fireball. Its damage is getting less impressive relative to enemy hit points, but damage is still damage, so if you can hit a lot of targets, it’s still worth using. Bless is still a solid option for concentration if you don’t want to use a higher level slot and/or your other spells don’t fit the situation, since it’s pretty much always good. Command is still a go-to non-concentration option that can be cast at any level. Keep in mind though that spell slots you can avoid spending in combat can be used to rest cast aid.

Level 10 Cleric

Divine Intervention – You have a 1 in 10 chance of getting your deity to offer their assistance in a dire situation (well, it doesn’t have to be a dire situation, but since you can’t use this again for 7 days if it works, you probably don’t want to use it for a free sandwich). The odds of success aren’t high even if the impact would be great, so this is probably not something you want to use an action on in combat very often, but if the party has big goals out of combat that would be difficult to accomplish otherwise (things like resurrections of targets who’ve been dead too long to bring up with spells you have access to), especially if they’re things you can do during downtime, you may as well give this a try. And of course, if the party is about to die, this is where the term “Hail Mary” comes from.
Spell Changes: +death ward, +thaumaturgy, -stone shape.

Death ward – Like aid, this is an 8 hour duration spell that can be rest cast with any 4th or 5th level slots you have at the end of the day. Using your highest level slot on aid is still likely the first priority for rest casting, but you may as well use this on as many allies as you can with other remaining slots.
Animate dead – Most spells that give you extra creatures to control require concentration; this is one of the few exceptions. Having a few skeleton archers follow us around is a nice little bit of extra damage without a big resource commitment: just a 3rd level slot each time you want to animate a new one, and then a single 3rd level slot each day to maintain control over up to four of them. We are at a point now where we can afford to commit a 4th or 5th level spell slot to either spirit guardians or banishment in any important fight, making it more likely you’ll have some spare 3rd level slots. If so, this is a cheap ongoing offensive boost. The skeletons are fragile, but if you can bring the bones with you and cast the spell at camp, the value you get is usually from slots that would have gone unused otherwise, so it’s almost free damage. Yesterday’s unspent 3rd level slot normally does zero damage and animate dead fixes that. Plus, you can probably just reanimate them out of combat after they’re killed anyway.
Thaumaturgy – This is mostly something to enhance your ability to roleplay a powerful being with a link to the divine, as it doesn’t have defined mechanical benefits, but DM-willing you might be able to use it to make yourself more intimidating, create distractions, or trick people.

Level 11 Cleric

Destroy Undead (CR 2) – Now featuring ghasts, minotaur skeletons, poltergeists, and will-o’-wisps, among other things.
Spell Changes: +heal.

Heal – This one’s pretty straightforward: you heal yourself or an ally for 70 HP. Unlike most Cleric healing spells that aren’t aid or a 1st level healing word, this one is actually pretty impactful for the spell slot (although an upcast banishment stands a good chance of preventing more damage than this heals if you use it against the right targets). This spell gets relatively better compared to control options the stronger your party’s defenses are. In terms of total hit points healed, an upcast aid provides slightly more, but if the enemies are focusing their damage, it’s useful to be able to concentrate the healing in one place.

Level 11 Strategy

It’s probably worth being a bit stingy with your 6th level spell slot in case you find yourself needing to cast heal. But you probably have enough 4th and 5th level slots to use one in any fight if you need to, which means you can basically always be upcasting spirit guardians to 4th or 5th or upcasting banishment to 5th, which frees your lower level slots for non-concentration things like fireball, command, or dispel magic. There’s also little reason not to cast divination rituals at the end of any day if you haven’t done so already. Information is power.

Level 12 Cleric

Ability Score Improvement – +1 Con, +1 Wis. Taking a split Ability Score Improvement here gets us to 18 in both Constitution and Wisdom, improving our durability and further improving our concentration saves, and increasing our spell save DC and number of spell preparation slots.
Spell Changes: +heroes’ feast, +greater restoration.

Heroes’ feast – If you’re playing in a game where gold flows freely, stock up on gem-encrusted bowls (the material component for this spell) and cast it every night before the party goes to bed if you haven’t used your 6th level slot. Or, provided nobody is secretly a Mogwai, cast it into the rest to give everyone a midnight (or 5am) feast, powering them through the next night’s rest. Advantage on Wisdom saves, immunity to poison and the frightened condition, and an increase to everyone’s maximum hit points (which stacks with those from aid, as, unlike with temporary hitpoints, there is no rule preventing this type of hitpoint buff from stacking) is a very nice package indeed. If gold is scarcer in your game you might not be able to do this every night, but if you know you’re facing a green dragon the next day, this is an instant win button. It’s well worth it if you expect to face any kind of big enemy that affects the mind; Wisdom saves are by far the most common of the mental saves.
Greater restoration – This is useful for somebody in the party to have on hand. A lot of the debuffs this clears are things that could be dealt with the next day, by prepping this when you know you need it, but there are some pretty nasty effects imposed by specific monster abilities that charm their target, and having this available if one of those sticks could really turn a fight around. The spell consumes 100gp of diamond dust, so make sure to have some on hand.

Level 13 Cleric

Spell Changes: +conjure celestial, +divine word, -bless.

Conjure celestial – This spell really ought to just be called “conjure couatl”, since that’s what you’re using it for. Listed at a mere CR 4, the couatl punches well above its weight, featuring a number of handy spells, a high AC that gets higher with the benefit of its 3/day shield spell, immunity to nonmagical physical damage from attacks, a 90’ flying speed, and a bite attack that can render enemies who aren’t immune to poison unconscious if they fail a DC 13 Constitution save. Most interestingly, its Change Shape feature gives it the ability to assume the form of any humanoid or beast of CR 4 or below. It doesn’t get the class features of its new form, which means it can’t benefit from the Spellcasting trait (defined in the Monster Manual as a class feature), but Innate Spellcasting may be fair game depending on how your DM interprets “gains statistics and capabilities that the new form but it lacks”: the couatl has its own Innate Spellcasting trait, so if a “capability” is construed as a named feature, then it doesn’t lack this, but if it’s more fine-grained, then it may be able to gain an Innate Spellcasting trait that provides different spells, or at least gain the new spells. One notable form that is useful without relying on spells is the wereraven, whose Regeneration ability can be used to keep the couatl alive (the couatl keeps its own HP and damage immunities, so if nothing else, do this between fights to get back to full health). Be aware that conjure celestial has a one minute casting time, so you won’t be able to cast it in combat.
Divine word – All of the power of this spell is in the last sentence. The hitpoint-gated status effects are pretty underwhelming, since at this level of play, by the time an enemy has hit points that low, they can likely be killed with at-will attacks or much lower level area-of-effect spells. But in a situation where you’re facing celestials, elementals, fey or fiends, a bonus action multi-target banishment that doesn’t require concentration is well worth the spell slot.

Level 13 Strategy

Ideally you can team up with an ally with access to planar binding so that you can have a couatl friend accompanying the party without using up your concentration (in which case you may want to prepare magic circle). But failing that, it still might be worth casting it if you are going into a boss fight. Not only is the couatl helpful for mobility, offense and defense in combat, but it can also pre-buff the party with its spells. That said, using conjure celestial means you won’t be able to use divine word, so assess whether you’re likely to run into the category of creature that the latter works well against, and judge which will help you more.

Level 14 Cleric

Destroy Undead (CR 3) – Mummies, wights, and sword wraith warriors, among many other setting- and adventure-specific undead, join the club of creatures that are instantly dusted for the crime of not rolling high enough on their Wisdom save.
Spell Changes: +freedom of movement.

Freedom of movement – Our existing options are likely to be better uses of our highest level slots than anything new we could pick up, so we take a situational spell which is very good in its situation. Restricted mobility is a leading contributor to adventurer death, and this spell prevents most forms of that. The text suggests that the protection from becoming paralyzed, restrained, or having speed reduced is prophylactic only, so this may be better to use proactively than reactively most of the time, though it’s worth asking how your DM interprets it. There are cheaper ways than a 4th level spell to break a grapple, so it’s primarily the other kinds of movement restrictions that you’d want this for.

Level 15 Cleric

Spell Changes: +holy aura.

Holy aura – There are some fights where you don’t want to get close enough to the enemy to use spirit guardians if you can help it, and where banishment is less effective because of Legendary Resistances. Fights this tough are what this spell is made for. It  imposes disadvantage on all attacks against all of your allies and gives them advantage on all saves, provided they are within 30’ of you. It has an extra effect against undead and fiends, who can be blinded if they manage to hit with attacks anyway. At this level, threats that merit an 8th level spell slot can probably hit most PCs with attacks even with disadvantage (though all but removing the risk of crits is valuable), but giving them advantage on saves can be a big deal, especially if there’s also a paladin giving them a +5. This has a 1000gp material component, though it’s not consumed.

Level 16 Cleric

Ability Score Improvement (Feat) – Alert. Initiative tends to be underrated. Many of our spells are not heavily dependent on having a high DC, so boosting our casting stat doesn’t offer as much value as it would on, say, a Bard or Warlock, but a +5 initiative makes the difference between having our round 1 spell up when a given enemy acts for the first time and not having it up about a quarter of the time. Many of our spells can prevent enemies from harming the party: banishment and divine word remove them from the battlefield, having holy aura up when a dragon breathes can prevent significant damage, and even spirit guardians can prevent attacks by slowing movement. But if the enemies have already made their big round 1 moves before we’ve had a chance to act, the effectiveness of those spells is greatly diminished. If you have another character in your party that regularly summons creature in the middle of combats, you may wish to skip Alert to deconflict that strategy with your spirit guardians. We recommend +2 Wis for that case. If you decide to significantly vary your preparations from what we recommend with this build in order to focus much more on spells that force saving throws, capping your Wisdom would also be a solid pick here.
Spell Changes: +antimagic field.

Antimagic field – Most of the biggest threats at high levels are magical in one way or another, and this can nullify them, provided you can get within 10’. Of course, it also nullifies your party’s ability to affect the area with magic, including magic weapons, so you’ll need to carefully weigh the costs and benefits. One option you might have when facing a powerful enemy who depends on magic is to ready movement to get within 10’ of them right before they act, and then use movement on your turn to move away (or vice versa, depending on the initiative order). That way your allies can still target them with magic when they’re not in the field, but they are hampered on their turns.

Level 17 Cleric

Destroy Undead (CR 4) – Banshees, bone nagas, flameskulls, and ghosts are among the undead who join the destructible club at this level.
Corona of Light (Light Domain feature) – You can create an aura of sunlight around yourself as an action. It lasts for a minute and gives enemies within 60’ of you disadvantage on saves against spells doing fire or radiant damage. That would be a pretty underwhelming effect if you got it at a much lower level considering that damage spells usually do half damage on a save anyway, and at this level when your damage spells do piddling damage relative to enemies’ hit points to begin with, it’s not worth an action in combat for that effect. However, if you’re facing enemies that are adversely affected by sunlight, such as vampires, then this is nice to have, especially since it doesn’t require concentration.
Spell Changes: +mass heal.

Mass heal – Being able to divide 700 hit points of healing however you want, and considering that even the bulkiest PCs like high level Barbarians only have 200 or so hit points, this spell will almost always translate to “heal everybody in the party, and probably any summons too, to full”. Hopefully you cast aid and maybe heroes’ feast the night before, since both provide healable increases to allies’ health pools.

Level 17 Strategy

In combat you’re likely using spirit guardians or banishment if it’s a “normal” fight, conjure celestial cast before a stretch of tough fights when you have prep time (if your couatl isn’t bound with planar binding already), holy aura in especially tough fights, and possibly the occasional antimagic field in niche situations. Once concentrating, your go-to options are still upcasting command (when it applies), possibly placing a guardian of faith bug zapper or two, and responding to the situation with a well placed dispel magic, freedom of movement, as well as the occasional heal. If things have really gone south and the party has taken lots of damage, you now have the ability to wipe the slate clean with mass heal. Out of combat you still have divination rituals and locate object, and you have night-time buffs like heroes’ feast, death ward, and your old stand-by, aid.

Level 18 Cleric

Channel Divinity (3/rest) – A 50% increase to your Channel Divinity uses. You get an extra daily use of Harness Divine Power as well, which means an extra 3rd level spell slot. Not a massive boost considering how many spell slots you have, but nice to have.
Spell Changes: +holy weapon.

Holy weapon – Sometimes you fight a single powerful enemy with Legendary Resistances and high mobility, and your concentration might be best spent boosting the single-target damage output of a weapon-using ally. The best recipient of this spell is an ally who makes a lot of attacks and hits with them reliably.

Level 19 Cleric

Ability Score Improvement (Feat) – Lucky. Being able to reroll important saves is never not useful.
Spell Changes: +planar ally.

Planar ally – This spell has a lot of flexibility, both on the player side and the DM side. You can ask a creature to help you in or out of combat as long as you pay them for their services, and at this level the suggested gold costs of the payment should not be a major barrier in most campaigns. That said, the DM can decide that the creature you are trying to hire will turn down your request, so this is another spell that you might want to discuss with the DM before you try to use it, to get a sense what kinds of services they are comfortable with you asking for.

Level 20 Cleric

Divine Intervention Improvement – You no longer have to roll when you beseech your deity to intercede on your behalf; it now works automatically (you can still only get the benefit once a week, which, since most campaigns don’t spend a ton of time at level 20, likely means once). A solid capstone, as increasing the success chance of Divine Intervention from 19% to 100% means you can use it in combat without a risk of your valuable action doing nothing.
Spell Changes: +gate.

Gate – With luck you’ve made some powerful allies on other planes by this point, and can invite them to assist you while paying their travel expenses for them in the form of a 9th level spell slot.

Level 20 Strategy

The biggest change is to the way we approach Divine Intervention now that it works with no roll (albeit only once per week). Possible uses are limited only by your creativity and your DM’s flexibility, but if nothing else, you should be able to use it to replicate the effect of any Cleric spell. Unlike wish, there is no restriction on the level of the spell effect this can replicate, so if the party can use mass heal twice in some particular day (which probably means a lot has gone wrong), you can now supply that. It’s also worth noting that using this for a spell effect does not involve you actually casting the spell (which is another difference between this and wish), which means that if the spell normally requires concentration, it shouldn’t here. So you could, for example, use this to produce the effect of holy aura while you also concentrate on something else. Moreover, antimagic field has a special exception for magical effects created by a deity, so you can shut down other magic near you by casting that yourself, giving you a monopoly on benefitting from magic in the area.