Mariachi

Mariachi is a robot hamster that appeared in the Short Circuits section of Mega Man #9. He was created by Dr. Light for unknown purposes, though "for fun" cannot be ruled out. As Mariachi runs, his wheel charges a battery, and the battery powers Mariachi, creating a perpetual motion machine. Proto Man then tells Mega Man, "And people wonder why I didn't want him messing with my power supply."

Trivia

 * The name of the robot hamster is most likely a reference to the Mexican genre of music, continuing the theme of the original series Mega Man characters being given music-related names.