Brain Golem

Immutable Form. The golem is immune to any spell or effect that would alter its form.

Aversion of Decay. If the golem takes necrotic damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.

Psychic Absorption. Whenever the golem is subjected to psychic damage, it takes no damage and instead regains a number of hit points equal to the psychic damage dealt.

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

Magic Weapons. The golem's weapon attacks are magical.

Multi Attack. The golem can make two slam attacks in a turn

Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage.

Mind Blast (Recharge 5–6). The brain golem magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 15 Intelligence saving throw or take 22 (4d8 + 4) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.