Coral Elemental Protector

Reef Glide. The elemental can burrow through nonmagical, underwater reef and ocean floor. While doing so, the elemental doesn't disturb the material it moves through.

Siege Monster. The elemental deals double damage to objects and structures.

Underwater Camouflage. While still and amongst a coral reef, the elemental is almost indistinguishable from the reef itself.  It gains advantage on stealth checks and perception checks against it are made a disadvantage.

Coral Growth.  The Coral Elemental can grow a maximum of 1d6+2 appendages and each appendage can be no longer or taller than 60ft.  Each appendage has 50 HP and can not be regrown once it is destroyed. As an action, for a speed of 20ft per round, the elemental can expand and grow its coral appendages in any direction.  The elemental can grow and expand any or all of its available appendages each turn.

Multiattack. The coral elemental makes two slam attacks OR three slash attacks.

Slam. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 18 (2d10 + 5) bludgeoning damage.

Coral Slash. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 15 (2d6 + 8)  slashing damage.

The Elemental Coral Protector can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The elemental regains spent legendary actions at the start of its turn.

Coral Cut. Lash out with an appendage and attempt to strike a target within 10ft of the appendage.

Coral Absorb. Grab one creature within 10ft of an appendage.  Make an opposed grapple check, upon success, the target is grappled and takes 2d6+5 piercing damage from hollow coral spines.  The elemental regains half the damage as healing.  At the end of the grappled creatures turn, repeat the 2d5+5 unless the grapple is broken.  Only one creature may be grappled by an appendage at a time.

Prime Slam. (Costs 3 Actions). All remaining appendages raise up and slam into the ground.  Any creature within 20ft of an appendage must make a Dexterity saving throw (DC 19) or take 2d12 bludgeoning damage and be knocked prone.  If the creature is successful, they take half damage and are not knocked prone.