Kenko

Kenko the Shapeshifter appeared as the main villain of the Sumo Slammer Smackdown video game in Game Over. He is a shapeshifter and archenemy of Ishiyama, the hero of the game. He overhears Ben talking about the Upgrade token; believing it could be used to allow him to take over the real world, he attempts to obtain it. While Ben searches for the token, he fights and defeats Ishiyama, then assumes his nemesis' form after Ben reaches the Upgrade token first. He tries to trick Ben into taking him to the real world, but Grandpa Max's timely intervention in the game reveals his ruse. As Upgrade, Ben's control over the game allows him to depower Kenko, revealing him to actually be a small, weak, human-like creature. Afterward, Kenko is defeated when he knocks himself out by accidentally hitting himself in the head with a piece of his own armor.

Ben 10: Alien Force
Kenko was mentioned in The Final Battle: Part 1, when Ben mentions that in a sequel to the first Sumo Slammers series called Sumo Slammers: Hero Generation, taking place 5 years later, he teamed up with Ishiyama. This, as well as the title was Alien Force's working title and the other descriptions Ben gave, is a self-parody of Alien Force itself due to Kevin teaming up with Ben in Alien Force.

Ben 10

 * Game Over (first appearance)