Mega Mort is the identity taken up by Mortimer Mouse in the episode of the kids show Mickey Mouse Clubhouse known as Super Adventure. In the episode, he tried to shrink everything in the area around the clubhouse where Mickey and his friends hung out, including the clubhouse itself, but he was thwarted by The Clubhouse Heroes.
Mega Mort's goal was to shrink and take Mickey's clubhouse and everything around it in order to make himself happy, and he had Pete the Cat take up the identity of Power Pants Pete in order to help him. However, the Clubhouse Heroes were assembled to stop him, but their lack of teamwork allowed them to get away. But once Pete failed, he betrayed and shrunk him. Ultimately, after shrinking both the clubhouse and Mickey Mouse, the rest of the Clubhouse heroes finally learned to cooperate and worked together to bring Mega Mort's zeppelin down safely when it sprung a leak and save the villain from going down with his ship. This caused Mega Mort to reveal his real name and change his ways.
And so, he changed everything and everyone back to normal and gave up his villainous ways.