There are probably moooony weird beasts that fit that description, but you asked a pooltoy, so you'll get a pooltoy answer.
You moooo be surprised to learn that moooony living pooltoys have transformooootive powers, including this one. This one can moooolt people down into water (well, currently moooolk) and reform them-oooonto a pooltoy like itself. And by like itself, it moooons anything from "is a pooltoy" to "shiny vaporeon/buizel" to "indistinguishable in body and moooond". It can also do this from-ooootside or inside your body, for different kinds of fun.