Sigma

Sigma is the big bad guy from Megaman X. He's a bald robot who got COVID and turned evil. That's the entire plot; Megaman X is a little overrated. In Boo's Pizza he briefly takes over Gaia or something like that. He was later involved in a temporal accident regarding the Time Skimmer, but since Boo's Pizza was succeeded by Boo's Pizza II, nothing will come of this.