Priest

A priest on the party's side is the campaign cleric NPC made flesh: a temple contact, a hired chaplain for a long expedition, or the local rector of a town the party has saved. She is not a combat hireling first. She is a moral authority with a mace, and your job is to give her the scenes that show both halves of that.

Out of combat she is the party's medical officer and their conscience. Lesser Restoration via Divine Aid (3/Day) clears a paralysis, blindness, deafness, or one disease, which is exactly the resource a low-level party never wants to spend its own slots on. Healing Word at 30 ft. picks up a downed PC at the start of any round. Dispel Magic in the bonus-action slot ends a curse or a Hold Person on the rogue. Medicine +7, Religion +5, and Perception +5 make her useful in any temple, ruin, or interrogation.

In combat, lead with Bless on the two melee PCs as a bonus action. That is the play that earns her the next session's invitation. On round two, drop Spirit Guardians (1/Day) when the party is engaged with multiple enemies and the priest can stand at the back of the front line. The 15-foot aura tags every adjacent enemy for 3d8 radiant a turn at half speed, which usually wins the fight outright. After the spell, Multiattack with Radiant Flame at range, since she should not be in melee with 38 HP and AC 13.

What she refuses: striking a surrendered foe, lying under oath, killing a child of any race. If the party asks her to break one of these, she leaves at the end of the contract.

Roll her Healing Word check in the open the first time she revives a player. The party should see a friendly priest as the difference between a TPK and a story.

A priest is a CR 2 NPC that punches like a CR 4 the moment Spirit Guardians comes down. The whole encounter is built around that one spell, and a GM who forgets it has been handed a chain shirt with a mace. Open the encounter knowing the priest will burn the 1/Day Spirit Guardians on round one if the party is grouped, or hold it for round two if the front line has not yet engaged.

Spirit Guardians at 3rd level fills a 15-foot radius around the priest with 3d8 radiant damage on a failed DC 13 Wisdom save (half on success), and creatures in the aura have their speed halved. The priest is now a moving denial zone with 38 HP. Walk into the cleric, the wizard, the paladin holding the line; force three saves a round. Concentration is the lever the party has, so play accordingly: the priest moves with allies between herself and ranged attackers, and on any successful Concentration save she advances. Bonus-action Divine Aid casts Bless on the two best fighters in her formation if available, or Healing Word at 30 ft. on a downed ally; both burn the bonus action without breaking concentration.

Multiattack on her turn is two of any combination of Mace and Radiant Flame. Mace at +5 deals 11 average (6 bludgeoning plus 5 radiant), Radiant Flame at +5 from 60 ft. deals 11 radiant. The melee option is for finishing a downed target while Spirit Guardians ticks; the ranged option is for the back-line caster who has been keeping their distance. Aim Radiant Flame at whoever has shown the most healing or buffing this round.

Priests with Spirit Guardians up do not retreat. Without the spell they fall back to their congregation, throw Healing Word at a wounded ally, and yield once two of the squad are down. Surrender is an option; she has Religion +5 and will negotiate.

Telegraph Spirit Guardians with a chant and a ring of shimmering shapes around her. The party should hear it cast, see the speed-halving aura, and know exactly what is killing them.