Coral Golem(shared version)

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

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

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

Regeneration. The golem regains 10 hit points at the start of its turn if it is submerged in salt water. This trait does not function if it took acid damage in the last round. 

Multiattack. The golem makes two  coral slam attacks.

Coral Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 22 (3d8 + 10) bludgeoning damage.

Coral Eruption (Recharge 5–6). The golem targets the area within 25 feet of it. Each target must make a DC 18 Dexterity saving throw against this effect. On a failed save, a target can't use reactions, its speed is halved, and takes 8d8 bludgeoning damage or half on a success.

Tidal Wave (Recharge 9-10). The golem conjures a wave of water up to 30 feet long, 10 feet high, and 10 feet wide. Each creature in the area must make a DC 17 Dexterity saving throw against this magic. On a failed save, a target takes 18 (4d8) bludgeoning damage and is knocked prone. On a successful save, it takes half damage and is not knocked prone. The water then spreads across the ground, dousing unprotected flames in its area and within 30 feet of it.