Me and my friend were playing when we realized that when there's two controllers plugged in, each controller controls the character and we tried to beat the game as this and we did, you can still do any% and 100% with this so I'd think this would be really cool to do.

That in of itself is interesting. Can you provide an example?

Could be fun at a marathon, 2p1c becomes 1 character, 2 controllers

What happens if one does not do anything? What rules would it have?