Star Spawn, Larva Mage

A larva mage is a nightmarish combination of a mortal body and otherworldly substance. When a powerful cultist -usually a warlock or other spellcaster- contacts the comet-borne emissary of some dark god, the emissary can merge with a mortal consciousness to create a larva mage. None of the original cultist's personality survives the transformation, so what emerges is wholly alien.

Star Spawn Worm that Walks CR: 16

Medium aberration, chaotic evil

Armor Class: 16

Hit Points: 168

Speed: 30 ft

STR

17 +3

DEX

12 +1

CON

23 +6

INT

18 +4

WIS

12 +1

CHA

16 +3

Saving Throws: Dex +6 1d20+6 , Wis +6 1d20+6 , Cha +8 1d20+8

Skills: Perception +6

Damage Resistances: cold; bludgeoning, piercing, and slashing from nonmagical attacks

Damage Immunities: psychic

Condition Immunities: charmed, frightened, paralyzed, petrified, poisoned, restrained

Senses: darkvision 60 ft., passive Perception 16

Languages: Deep Speech

Challenge Rating: 16

The larva mage's innate spellcasting ability is Charisma (spell save DC 16, +8 1d20+8 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: eldritch blast (3 beams, +3 bonus to each damage roll), minor illusion

1/day: circle of death

3/day: dominate monster

Return to Worms. When the larva mage is reduced to 0 hit points, it breaks apart into a swarm of insects in the same space. Unless the swarm is destroyed, the larva mage reforms from it 24 hours later.

Actions

Slam. Melee Weapon Attack: +8 1d0+8 to hit, reach 10 ft., one target. Hit: 7 (1d8 + 3) 1d8+3 bludgeoning damage, and the target must succeed on a DC 19 Constitution saving throw or be poisoned until the end of its next turn.
Plague of Worms (Recharge 6) 1d6 . Each creature other than a star spawn within 10 feet of the larva mage must succeed on a DC 19 Dexterity saving throw or take 22 (5d8) 5d8 necrotic damage and be blinded and restrained by masses of swarming worms. The affected creature takes 22 (5d8) 5d8 necrotic damage at the start of each of the larva mage's turns. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Reactions

Feed on Weakness. When a creature within 20 feet of the larva mage fails a saving throw, the larva mage gains 10 temporary hit points.

Legendary Actions

The larva mage 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. The larva mage regains spent legendary actions at the start of its turn.
Cantrip (Costs 2 Actions). The larva mage casts one cantrip. Slam (Costs 2 Actions). The larva mage makes one slam attack. Feed (Costs 3 Actions). Each creature restrained by the larva mage's Plague of Worms takes 13 (3d8) 3d8 necrotic damage, and the larva mage gains 6 temporary hit points.