Water Elemental

If the monster takes Cold damage, its Speed decreases by 20 feet until the end of its next turn.

The monster can enter an enemy's space and stop there. It can move through a space as narrow as 1 inch without expending extra movement to do so.

The monster makes two Slam attacks.

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage. If the target is a Medium or smaller creature, it has the Prone condition.

Strength Saving Throw: DC 15, each creature in the monster's space. Failure: 22 (4d8 + 4) bludgeoning damage. If the target is a Large or smaller creature, it has the Grappled condition (escape DC 15). Until the grapple ends, the target has the Restrained condition, is suffocating unless it can breathe water, and takes 9 (2d8) bludgeoning damage at the start of each of the monster's turns. The monster can grapple one Large creature or up to two Medium or smaller creatures at a time with Whelm. As an action, a creature within 5 feet of the monster can pull a creature out of it by succeeding on a DC 15 Strength (Athletics) check. Success: Half damage only.