Abyssal Rotfiend

Abyssal Fields. Other creatures can not teleport away from the abyssal rotfiend while they are within 30 feet of it, nor can creatures teleport to a destination that is within 30 feet of it.

Magic Resistance. The abyssal rotfiend has advantage on saving throws against spells and other magical effects.

Innate Spellcasting. The abyssal rotfiends spellcasting ability is Charisma (spell save DC 19, +11 to hit with spell attacks). The rotfiend can innately cast the following spells, requiring no material components:

At will: darkness, animate dead, shadow of moil

3/day each: contagion, negative energy flood

Multiattack. The abyssal rotfiend makes two attacks with its Skullsplitter or Conjure Abcess. It can replace one of these attacks with either Floating Despair or its spellcasting.

Skullsplitter. Melee Spell Attack: +11 to hit, reach 5 ft., one target. Hit: 28 (4d10 + 6) psychic damage.

Conjure Abscess. Ranged Spell Attack: +11 to hit, range 60 ft., one target. Hit: 19 (3d8 + 6) acid damage and the target grows a sizzling abscess full of boiling pus that falls off at the start of the rotfiends next turn. If they use any form of their movement before that time, it bursts and deals 21 (6d6) acid damage to them, and each creature within 10 feet of them also must succeed on a DC 18 Dexterity saving throw or suffer the same damage, taking half as much damage on a successful save.

Floating Despair (Recharge 5 - 6). The abyssal rotfiend casts the darkness spell with its innate spellcasting feature, without needing to center it on a creature or object. As long as the rotfiend concentrates on it, humanoid creatures that start their turn inside of, or moves through this darkness for the first time on a turn takes 14 (4d6) necrotic damage from shadowy tentacles that lash at them. The rotfiend can use its bonus action to move this area of darkness up to 30 feet on its turn.