Actions

Multiattack. The creature can use its Life Drain ability or make 1 Claw attacks and then use Devour Intellector Dispelling Bite.

Claws. Natural Weapon. +4 to hit.
Hit. 9 (2d6+2) Slashing damage.

Dispelling Bite. After hitting with a Claw attack, the creature can cause spells of Level 2 or lower to be dispelled, making an INT check for each higher level spell.

Devour Intellect. The parasite teleports into one creature it can see within 10ft of it that has a brain. The vitcitm must then succeed on a DC 12 INT save or take 11 (2d10) psychic damage.
Also on a failure, roll 3d6+2: If the total equals or exceeds the target's Intelligence, the parasite subjects it to either a Dominate Person until removed or Feeblemind. and the host body is stunned until it makes a DC 12 CON save at the end of each minute as the parasite learns to operate its new body.
After taking over, the parasite knows everything the host knew, including spells, languages, and class features.
The host may attempt to reject the parasite up to three times by repeating the INT check as an action. However, after the third failure, they can no longer resist.
If the host body makes the initial INT save or drops to 0 hit points, the host may a free attempt to evict the parasite. On success, or on the host's full death, the parasite is ejected and teleports to a space within 5ft with 23hp.
The parasite may also be forced out if the host is subjected to Psychic damage, forcing the parasite to make a CON save vs half the damage. The parasite may also leave willingly (with full HP) with 20ft of movement.

Life Drain. Melee Spell Attack: +4 to hit, auto-crit vs Host.
Hit. 11 (2d8+2) Psychic damage. The target must also pass a DC 12 INT Save its HP Max reduced by the same.This reduction lasts until the victim finishes a long rest.
If this effect reduces the victim's HP Max to 0, they fully die, and their corpse is cursed and cannot be resurrected while the parasite lives.