Water weird
From Ardrana
Water weirds are strange creatures from the Elemental Plane of Water which are hostile when encountered on the Prime Material Plane, as they are usually magically kept from going home. If communication is achieved, a bargain can sometimes be struck with the creature.
Water weirds appear to be common water. When a water weird detects a living being, it assumes serpentine form and attempts to pull the creature into the water.
Note: Water weirds originally appeared in this form in the 2nd Edition Monstrous Manual for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.