So, I don't know if it's a dumb question or not, but I was wondering if is there any rule about doing an MP6 run in Multiplayer. Are there any category that you can do it or it's just against the rules?

While it seems like this game has all the runs be one player only, I noticed that MP7 Has a category for one player w/two controllers.

Yeah it's not actually multiplayer, but still, it's the closest thing since I don't think anyone does multiplayer with these games in speedrunning.