The Most Evil Koopa in the World is a SpongeBob fanon episode. In this episode, Bowser returns and Plankton causes trouble for him.
Sheldon J. Plankton
Eugene H. Krabs
Bowser is coming back to the Bikini Bottom. SpongeBob and Patrick are not very happy about this, seeing that they know Bowser is troublesome.
The next day, Bowser comes back and Plankton teases Bowser as he's not as evil as him and often lacks evil plans, so he boasts he can be even worse than him. Bowser then arranges an evil plan of destroying the Chum Bucket as revenge to Plankton for teasing him, but soon finds he is unable to do it, so Bowser decides to use his airships instead. He powers up so much energy for the cannons that they break loose and fall into the Krusty Krab. Yoshi arrives at the Bikini Bottom with Eugene H. Krabs, who is cross with Bowser, and forces him to leave Bikini Bottom in disgrace.
Yoshi then heads back to his home. And SpongeBob and Patrick all agree that even Plankton can be helpful sometimes, like helping to get rid of Bowser.