Bádh Bahar

Regeneration: The Golem heals for 50 hit points every turn unless it takes fire damage. 

Susceptible to Fire. If the golem takes bludgeoning damage in a turn, it becomes vulnerable to fire damage before it's next turn, which keeps it from healing. Fire Bad.

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

Lightning Absorption. Whenever the golem is subjected to lightning damage, it takes no damage and instead regains a number of hit points equal to the lightning damage dealt. Why? Idk, cause magic. The electricity awakens all of the nasty bits inside of it and gets it moving.

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

Magic Weapons. The golem's weapon attacks are magical. A little bit of glitter like substance covers anyone who is grabbed or attacked by the golem. It's crushed abalone shells. This has no effect on combat mechanics.  

Multiattack. The golem makes three attacks. Two thrown attacks and one slam.

Slam. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 21 (4d8 + 4) bludgeoning damage.

Throw. The Golem makes a grapple check, if it succeeds, it can throw a character up to 60 feet. +13 to grapple checks. Thats like, 5d6 damage. 

Nerf options: Sometimes the attacks of the golem are reduced if it does a ton of damage.

Legendary Resistance 1/day: I HAVE TOO MANY PLAYERS. I mean, I think just throwing minions at them just bogs down the fight, so, just throw one of these in the mix.