Bone Golem

Berserk. Whenever the golem starts its turn with 20 hit points or fewer, roll a 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.

False Appearance. While the golem is not moving, it appears to be a mound of bones.

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

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

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

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.

Multi-attack. The golem makes two Slam attacks. 

Slam. Melee Weapon Attack: +6 to hit, reach 5ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage.

Hideous Laughter (Recharge 5-6). Each creature within 30 feet of the golem that can hear it must succeed on a DC 13 Wisdom saving throw or become Frightened for 1 minute. A creature that fails its saving throw by 5 or more is Paralyzed for the same duration. An affected creature can repeat the saving throw at the end of each of its turns. On success the effect ends. If a creature’s saving throw is successful, or the effect ends for it, the creature is immune to the golem’s Hideous Laughter for the next 24 hours.