Berserk. Whenever the golem starts its turn with 40 hit points or fewer, roll α d6 On a 6, the golem goes berserk. On each of its turns while berserk, the golem attacks the nearest creature it can see. If no creature is near enough to move to and attack, the golem attacks an object, with preference for an object smaller than itself. Once the golem goes berserk, it continues to do so until it is destroyed or regains all its hit points. When Berserk it gains one more attack .

The golem's creator, if within 60 feet of the berserk golem, can try to calm it by speaking firmly and persuasively. The golem must be able to hear its creator, who must take an action to make a DC 15 Charisma (Persuasion) check. If the check succeeds, the golem ceases being berserk. If it takes damage while still at 40 hit points or fewer, the golem might go berserk again.

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

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

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

Thought Fortess. If another creature attempts to read the creatures mind or attempts to cast command , charm person or suggestion on it they hear a very loud static noise and have to make a Wisdom saving throw DC 15. If they fail they take 2d4 psychic damage. If they succeed they know that it's immune to these kinds of spells and hear the voices of the creatures it has absorbed begging them to kill them. 

Multiattack. The golem makes two slam attacks.

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

Bite. Melee Attack: +7 to hit reach 5 ft ,one target .Hit 3d6+4

Grapple : If a creature is within 10ft of it , as part of the Action (counts as one attack) it can try to grapple it . The creature must succeed a DC 15 strength saving throw or be grapple and pulled towards the creature 5ft. The golem can grapple up to 4 creatures but it can only devour one at a time .

Devour: As a bonus Action it can begin to swallow the creature that is grappled .The creature can make 3 attempts to get out at the end of its turn DC 15 strength or be devoured and absorbed into the golem's body . At the beginning of grappled creature's turn it takes 2d4 acid damage. If the creature falls unconscious inside it next turn it is absorbed and the golem gains 2d6 HP back.

Absorb Flesh. As a bonus action if the golem moves directly on top of a dead body it can absorb it and gain 2d6 HP back . If the golem absorbs more than 3 dead bodies it gains another attack as it gains more limbs.

Mind Spike (5-6)

Casting Time: 1 action

Range: 60 feet

Anti-magic Reaction. The creature can cast counterspell 2 times .

It has 3 legendary Resistances 

Familiar Whispers. The creature starts intruding the minds of its victims and producing the voices of someone they knew telling them they are in danger . Any creature within 40ft of it must make a DC 15 Charisma saving throw or be frightened for 1 min . The creatures can attempt to shake it off at the end of their turn .