Bowser

Bowser is the king of the Koopa Kingdom, and is most infamous for constantly attempting to kidnap Princess Peach and defeat Mario. However, he's never been successful.

He seems to have connections to the shadowy figure from Pooh's Adventures of Super Mario Land.

He first appeared in the second episode of Pooh's Adventures Universe, where he attempted to break into Peach's Castle. However, Mickey successfully defeated him. Before he could interrogate him, though, Bowser disappeared.