Mind Flayer Union

Mindflayer takes control of PC that willing gave itself to the creature.

Languages Deep Speech, Telepathy 120 ft., Undercommon

Innate Spellcasting (Psionics). The mind flayer’s innate spellcasting ability is Intelligence. It can innately cast the following spells, requiring no components:  

At will: detect thoughts, levitate

1/day: dominate monster

Tentacles. Melee Weapon Attack: one creature. Hit: (2d10 + STR) psychic damage. If the target is Medium or smaller, it is grappled (escape DC STR) and must succeed on a (DC INT) saving throw or be stunned until this grapple ends.

Extract Brain. Melee Weapon Attack: one incapacitated humanoid grappled by the mind flayer. Hit: The target takes (10d10 + STR) piercing damage. If this damage reduces the target to 0 hit points, the mind flayer kills the target by extracting and devouring its brain.

Loss of Mouth: Character no longer has a mouth, all communication will be telepathic.