This is when a Video Game boss isn't teamed up or associated with the Big Bad. He's a lone wolf and isn't the main antagonist's Mook. He is an antagonist all on his own. This is relatively common in RPGs, where the player party often winds up just running into bosses that just happen to be at the end of caves, attacking a town, guarding MacGuffins, etc. Sometimes overlaps with Giant Space Flea From Nowhere.