Cataclysm

Cataclysm is an earth pony with a tail.

He's chaotic evil and enjoys bring pain and torture to those around him.

He's a prankester at heart and doesn't care what people think of him, worse case he'll prank them next.

His pranks tend to get out of hand, and most cases someone gets hurt 

He wears a freaky mask, most times but when he's not wearing it, he's still wearing it on his head and a wider smile is on his face