snakeopotamus
The most deceitful creature ever to trod this earth. They live solely to screw with people. Incredibly good as disguising themselves, snakeopotamusses blend into whatever environment they happen to be in and are difficult to spot. In their true form all snakeopotamusses are some combination of snake and hippo parts. One could be all hippo except for a little rattle on the end of his tail and another could be all snake except for an oversized hippo head. Any combination counts and no snakeopotamus has the same combination.
"That lady put Jell-O in my socks. She had awfully big teeth, I'll bet she was a snakeopotamus."