Cursed Golem

Magic Absorption. Whenever the golem is subjected to magic, it gains 2d8 extra damage on the next attack. (Stacks)

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

Magic Magnet . The golem automatically fails saving throws against spells and other magical effects.

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

Heavey Blows. The golem's attacks knock creatures smaller than it 10 ft away.

Cursed Fist. The golem's strikes inject cursed energy into its targets causing them to go mad temporarily if the target fails a Wisdom save (AC 14). A creature filled with madness will attack the nearest creature on its next turn. 

Multiattack. The golem makes two slam attacks.

Slam. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) bludgeoning damage. If the target is a creature, it must succeed on a DC 15 Constitution saving throw or have its hit point maximum reduced by an amount equal to the damage taken. The target dies if this attack reduces its hit point maximum to 0. The reduction lasts until removed by the greater restoration spell or other magic.

Haste (Recharge 5–6). Until the end of its next turn, the golem magically gains a +2 bonus to its AC, has advantage on Dexterity saving throws, and can use its slam attack as a bonus action.

Slow (Recharge 5–6). Until the end of the target's next turn, the target magically suffers a -2 loss to its AC, and has disadvantage on Dexterity saving throws.

Channel. The golem can channel cursed energy into its eyes before firing it at a target. If the target fails a Wisdom saving throw (AC 14) they have disadvantage on their next attack.