Acid Form. The elemental can move through a space as narrow as 1 inch wide without squeezing. A creature that touches the elemental or hits it with a melee attack while within 5 feet of it takes 2d10 acid damage. In addition, the elemental can enter a hostile creature's space and stop there. 

Freeze. If the elemental takes cold damage, it partially freezes; its speed is reduced by 20 feet until the end of its next turn.

Multiattack. The elemental makes two slam attacks.

Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 2d8 + 4 bludgeoning + 1d12 acid damage.

Acid Splash.  Ranged Weapon Attack: +7 to hit, reach 30ft.,The elemental throws a bubble of acid at a creature, on a hit it and any creature within 10ft. must make a Dexterity saving throw (DC 15) or take 2d8 acid damage.

Whelm (Recharge 4–6). Each creature in the elemental's space must make a DC 15 Strength saving throw. On a failure, a target takes 2d8 + 4 bludgeoning + 2d10 acid damage. If it is Large or smaller, it is also grappled (escape DC 14). Until this grapple ends, the target is restrained and unable to breathe. If the saving throw is successful, the target is pushed out of the elemental's space.

The elemental can grapple one Large creature or up to two Medium or smaller creatures at one time. At the start of each of the elemental's turns, each target grappled by it takes 2d8 + 4 bludgeoning + 2d10 acid damage. A creature within 5 feet of the elemental can pull a creature or object out of it by taking an action to make a DC 14 Strength and succeeding. On pulling them out they also take 2d10 acid damage.