There's categories for the different difficulties, but the only difference I see is the amount of health points and the presence of checkpoints. It doesn't seem like a fast run on Easy would be much different from a fast run on Hard, so it seems like more of a variable than a category. In addition, there's an "Expert" category that doesn't appear to exist, unless I'm missing something.

Okay, just found the Expert difficulty mode, though it seems like a Damageless category would be the same thing, like what we have for Super Mike Maker.