I used Yoshi, too. I must admit it took a million tries to pull it off, but I didn't have to use any holes in the AI. I couldn't force the metal enemy off the edge in an egg--Dr. Mario, it was. He kept making it back to the stage. I couldn't use PK Flash to dispatch the cowardly CP player you always get after the trophies bonus stage, obviously. Also couldn't use PK Flash when an enemy stopped moving in Brinstar. Didn't fight on Big Blue, where you can trick the CPU into walking right off the boundaries of the stage.