Nope. It's polygon man.
During rivalry cutscenes the background screams playstation. Just watch this.
That's just the style of the game. I don't think that has anything to do with the final boss. Until there's an actual screenshot by SuperBot, saying it is or isn't one thing isn't right, yo.
It wont be him for 2 reasons.
1. He is already in the backround of one of the levels (don't recall which one)
2. It's Polygon Man.
I was at theLA event and Seth was waering a shirt with Polygon Man, and I knew it would be the final boss when I saw that shirt.
Exactly, it is the style of the game. Polygon man is the only final boss that would explain why they are all there and fighting. With any other boss that cutscene would need a different environment or else it wouldn't make sense.