Would it be possible to make a sub-category for mirror mode times? As far as I'm aware all of the tracks in mirror are 150cc by default.

Would the category No Slaves be possible? Also, would adding The Ensign also be possible?

Weight class matters for a lot of the runs. I don't know if weight plays into speed, but I do know light-class characters get access to the barrel kart, which is one of the fastest karts in the game.