Yawgmoth, God of Phyrexia

Legendary Resistance (5/Day). If Yawgmoth fails a saving throw, he can choose to succeed instead.

Spellcasting. Yawgmoth is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 27, +19 to hit with spell attacks). Yawgmoth has the following spells prepared:

Cantrips (at will): acid splash, chill touch, frostbite, infestation, mage hand, poison spray, spare the dying

1st level (4 slots): cause fear, chromatic orb, command, disguise self, fog cloud, magic missile, ray of sickness, shield, false life, tasha's caustic brew

2nd level (3 slots): alter self, blindness/deafness, crown of madness, detect thoughts, enthrall, heat metal, magic weapon, misty step, ray of enfeeblement, shadow blade, suggestion

3rd level (3 slots): animate dead, bestow curse, slow, summon lesser demons, summon undead, vampiric touch 

4th level (3 slots): banishment, blight, death ward, evard's black tentacles, sickening radiance, summon greater demon

5th level (3 slots): bigby's hand, contagion, cloudkill, creation, dominate person, geas, negative energy flow  

6th level (2 slots): blade barrier, circle of death, create undead, disintegrate, eyebite, mass suggestion, soul cage

7th level (2 slots): dream of the blue veil, forcecage, power word pain 

8th level (1 slot): abi-dalzim's horrid wilting, antimagic field, maze

9th level (1 slot): shapechange, time ravage

Yawgmoth's Edict. Whenever a spell attack misses Yawgmoth or his saving throw against a spell succeeds, the caster of that spell takes 1d10 necrotic damage for each level of the spell, and Yawgmoth regains hit points equal to the necrotic damage taken.

Phyrexian Rejuvenation. When Yawgmoth drops to 0 hit points or dies, he dissipates in a cloud of darkness and is unable to take physical form until he returns to the core of Phyrexia. It takes him 1d10 days to return to Phyrexia and 1d12 months to gain a new body. If he is killed on Phyrexia, he cannot reform and dies permanently. 

 Multiattack. Yawgmoth makes three Vile Burst attacks.

Vile Burst. Melee or Ranged Spell Attack: +19 to hit, reach 15 ft. or range 150 ft., one target. Hit: 21 (2d10 + 10) necrotic damage.

Spread Affliction (Recharge 4-6). Yawgmoth chooses a diseased, paralyzed, or poisoned creature that he can see within 120 feet. That creature must succeed on a DC 27 Constitution saving throw. On a failed save the target takes 21 (6d6) necrotic damage, and each other creature within 30 feet of the target must succeed on a DC 27 Constitution saving throw. On a failed save a creature takes 10 (3d6) poison damage and is poisoned for 1 minute. A poisoned creature can repeat the saving throw at the start of each of its turns, ending the effect on a success.

Proliferate (Recharge 5-6). Yawgmoth targets any number creature he can see and who have taken either fire, poison, acid, lightning, physic, or necrotic damage during this combat. Yawgmoth deals 34 damage of that type to the targeted creatures. If a creature has taken multiple of these types of damage, Yawgmoth chooses which type to deal. 

Toxic Deluge (Recharge 5–6). Yawgmoth causes glistening oil to fall from above like rain in 150-foot radius around himself. Each creature in that area must make a DC 27 Dexterity saving throw. On a failed save, the creature takes 71 (11d12) necrotic damage. On a successful save, the creature takes half as much damage.

Phyrexian Rebirth (Recharge 6). Yawgmoth targets the corpse of one creature that isn't a phyrexian within 150 feet of him. The corpse returns to life with all its hit points. The creature is immediately compleated, becoming a phyrexian, and is charmed by Yawgmoth and obeys his commands.

Change Form. Yawgmoth transforms from one form into another. either his Human, Cloud, Wall or God form, he has no additional traits in his God form. His statistics remain the same except for the changes noted. 

Human Form: Yawgmoth's monster type becomes humanoid instead of undead, his size becomes medium, he gains the human subtype and his walking speed becomes 30ft. 

Cloud Form: Yawgmoth gains a flying speed of 120 feet and his Toxic Deluge recharges on a 3-6.

Wall Form: Yawgmoth's movement speed becomes 0 and his armor class increases by 2.

Yawgmoth can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Yawgmoth regains spent legendary actions at the start of his turn.

Cantrip. Yawgmoth casts a cantrip.

Vile Burst (Costs 2 Actions). Yawgmoth makes one Vile Burst attack.

Terrifying Presence (Costs 2 Actions). One target of Yawgmoth's choice within 150 feet of him must succeed on a DC 27 Wisdom saving throw or become frightened of Yawgmoth until the end of its next turn.

Arcane Sickness (Cost 3 Actions). Roll a d6. Yawgmoth takes necrotic damage equal to 10 x the number rolled, and then casts a spell from his list of prepared spells whose level is equal to or lower than the result, without expending a spell slot, and the spell is cast at a
level equal to the result.