Water Whizmo

Water Form. The elemental can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

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.

Whiz Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) bludgeoning damage.

Whiz Whack(Recharge 4–6). Each creature in the elemental's space must make a DC 12 Strength saving throw. On a failure, a target takes 6 (1d6 + 3) bludgeoning damage. If a creature fails, it is also grappled (escape DC 11). Until this grapple ends, the target is restrained and unable to breathe unless it can breathe water and takes 1d6 bludgeoning damage on each of its turns. 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 13 (2d8 + 4) bludgeoning 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 check and succeeding.

Absorb Projectile. As a reaction, the Water Whiz can absorb a projectile fired at it, reducing its damage by 1d8. 

The Water Whiz has 3 legendary actions per turn cycle that it can spend to do any of the following:

Whiz Slam (1 LA). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) bludgeoning damage.

Healing Current (2 LA). The whiz picks up more water from around the chamber, regaining 2d10 (10) HP.