Head Smash without cancelling the recoil usually doesn't end up well. Many believed Rampardos would be an unstoppable force with base 170 Atk and Head Smash, but being relatively fragile and slow, things didn't end up that way. Huge Power would be amazing, but that can be said for any species relying on physical moves. And since it would still have bad speed, I'd say it wouldn't rise too much, although I suppose a Rock Polish set could be pretty threatening.
Some more reasonable things it could get would be Rock Blast and Recover though. Former fits well with its physiology as it can just launch the stones it's composed of, and Recover hints towards its ability to replace its body parts with new rocks. Solid Rock as a hidden ability wouldn't be bad either.
But yeah, given its stats and typing, it's not meant for greatness, but some useful additions to its movepool could definitely land it a spot in RU or at least the top of NU.
