Freeze. Cold damage slows it by 20 ft until the end of its next turn.
Water Form. Can enter and stay in a creature's space, and slip through gaps an inch wide.
Actions
Multiattack. Two Slams.
Slam. A crashing wave that knocks a Medium or smaller target Prone.
Whelm. Recharge 4-6. Each creature in its space: DC 15 Str save or 4d8+4 Bludgeoning, held (escape DC 14), Restrained and battered 2d8 each of its turns.