If onlyMega Heatran
Cube sounds threatening as hell in this metagame. Running STAB earth power gives it a way to decimate steels while making it neutral to rocks, while STAB fusion bolt just gives another one of its physical moves raw power. You could probably get away with running a defensive typing and using subroost as well.
EDIT: Do you HAVE to run hidden power to change your type? Or do you just need to change your IVs? Having to run hidden power sounds kind of boring since it's so weak tbh.