Earthquake, Fire Punch, Play Rough and I wish it could get Drain Punch, but sadly no. So what move?
Why not Payback or Brick Break?
Payback compliments its low speed while Brick Break lets it function as a good screen breaker.
Another option would be Outrage.
Seems kinda redundant but after all things that wall Outrage are gone or Granbull is gonna die, does it even matter?
Another one: Power-Up-Punch
Goes well with Granbull's high attack stat and makes it sky high! :o
Hope I helped!
-It's a secret!
Ice Punch - Covers Ground flying and grass Pokemon.
Power Up Punch - Covers Ice and Normal + +1 Atk. each time it hits.
Brick Break - Covers Ice and Normal + shatters Barriers
Wild Charge - Covers Flying and Water.
Rock Tomb - Covers Flying, Ice, and Bug Pokes + -1 Speed to the Opponent.