I notice there's a 100% SMS category, but with no defined rules? What defines this, and can it be done on other versions of the game besides SMS?

The 100% Category includes:

All Legendary Equipment
Beating all Bosses (also the alternate Boss before Medusa - the Wizard)
Getting 10 Hearts (400.000 Points)
Finishing the Side Quest and get the Bell or Ruby

I think it can be also done in the Arcade Version. But nobody ever wanted to do a run in 100% there until now since Any% is hard enough and as I can see the runners mostly get a lot of legendary equipment anyway there in the Arcade Version.

Thanks much!