You’d think, if I wanted to provide the rules widgets to support deific sponsorship, that I’d use the cleric as a basis?
HAH! No. Paladins. Paladins represent a divine mixin already, after all: they’re the fighter-types who heed the call.
The PHB gives us 3 paladins oaths to work with (so we’ll be working on the Devoted, the Ancient and the Vengeful), and the DMG another one (the Fallen). There’s the oath of the crown in the sword coast adventurer’s guide, but as I write this post I don’t have easy access to it, so let’s pretend it’s dead to us.
The MM gives us angels — sort of “paladins-as-monsters” if you squint, with their aura of detect lies, their always-on radiant smites, their lay on hands, their various abilities. But they don’t really line up with the oath of devotion directly, since they’re made for a different purpose.
A Devoted creature smites (4d8, 5d8 or 6d8 radiant on weapon damage), is immune to charm and fear, resists radiant and mundane weapon damage, has magic resistance, has truesight, knows when it hears a lie, and can heal by touch (4/day, smite value + 5, 10 or 15 healed, and the subject also has any curse, disease, blindness or deafness conditions removed).
They can cast protection from evil and good, dispel evil and good, and commune. 1 each per day unless otherwise noted.
Their type becomes celestial.
An Ancient creature is immune to charm, sleep, poisoned and age, resists damage from poison and spells, has magic resistance, speaks all beast tongues, and has the trackless step (cannot be tracked, unaffected by natural difficult or hazardous terrain), siege creature (triple damage to constructs and objects), and regeneration 15 (, 20 or 30; suppressed by iron weapons) traits.
They can cast misty step (1/short rest), plant growth, and commune with nature. 1 each per day unless otherwise noted.
Their type becomes fey.
A Vengeful creature smites (4d8, 5d8 or 6d8 psychic on weapon damage), is immune to fear, has magic resistance, when it is reduced to 0 hit points may make a con save with DC equal to half the damage to be reduced to 1 hp instead, and has a 30-foot aura of menace (begin or enter, be frightened of the vengeful, wis save initial and each turn outside aura or damage negates for 24 hours; frightened creatures in the aura of menace grant advantage on attacks against themselves).
They can cast haste (1 per short rest) and scrying (1 per day).
A Fallen creature smites (4d8, 5d8 or 6d8 necrotic on weapon damage), is immune to charm and fear, resists necrotic and mundane weapon damage, has magic resistance, has truesight, and has a 30-foot aura of dread (dims light one step and imposes disadvantage on sight-based attacks; begin or enter, be frightened of the fallen, wis save initial and each turn outside aura or damage negates for 24 hours; frightened creatures in the aura of dread have vulnerability to all damage)
They can cast darkness, animate dead and geas. 1 each per day.
Their type is fiend.
The 4d8/5d8/6d8 values are pretty tier dependent, assuming a base CR of 10 and a top CR of 23 — I ripped them off the angels in the MM. So it’s probably something like “Just use your proficiency bonus in d8s”, though I haven’t actually checked that that’s how the math plays out.