Brainsucker

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

Innate Spellcasting. The brainsucker's innate spellcasting ability is Wisdom (spell save DC 15, +7 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: Charm Person, Disguise Self, Sleep
1/day each: invisibility, Darkness, Confusion

Insightful. The brainsucker gains points of insight by consuming the wisdom of other creatures. It can spend this insight to cast spells from the list below without any of the required material components.
Modify Memory (Costs 10 Insight).
Mirage Arcane (Costs 15 Insight).
Simulacrum (Costs 20 Insight).

Multiattack. The brainsucker makes two eldritch blast attacks.

Eldritch Blast. Ranged Spell Attack: +7 to hit, range 120 ft., one target. Hit: 6 (1d10) force damage.

Eldritch Grasp. The brainsucker fires a volley of up to three eldritch projectiles at creatures it can see within 60 feet. Each target must make a DC 15 wisdom saving throw. A creature that fails is restrained and can attempt another saving throw at the end of its turns.

Extract Insight. Melee Weapon Attack: +6 to hit, reach 5 ft., one humanoid that is grappled by the brainsucker, is restrained, is incapacitated, or is willing. Hit: 16 (3d10) piercing damage. The target creature's wisdom score is reduced by five, and the brainsucker gains five points of insight. If this wisdom reduction brings the target's wisdom below ten, the target must roll on the short-term madness table in the Dungeon Masters Guide. If this wisdom reduction brings the target's wisdom to a five or lower, the target must roll on the long-term madness table. If this wisdom reduction brings the target's wisdom to zero, the target is incapacitated and must roll on the indefinite madness table. The target's wisdom returns to normal after a short or long rest.