Quote from Cucurbita;1163751:
Tackle, Sand Attack, Sleep Talk, and Hidden Power Normal.
Edit: Dragon Dance, Outrage, Earthquake, and Stone Edge. Possible held items are choice scarf, life orb, lum berry, or yache berry. Dunno about Yache berry anymore though.
Garchomp can't learn Dragon Dance though as far as I can see. Nothing for TM's, breeding or Tutoring.
Anyways I think I'll go with Sword Dance, Fire Fang (coverage), Outrage + Lum Berry isn't too bad of an idea or I could go with Dragon Claw for the safer bet, and then Earthquake (coverage)
Btw, I tested my Tyranitar and Sylveon and Sylveon was doing great. Took out a Greninja with my toxic stalling. Guy I was fighting forfeited when he got down to his last pokemon and didn't break through Sylveon's substitute. He probably figured it would go down the same way it did with Greninja where he keeps trying to break through the substitute while I poison him and calm mind to finish him off with a Draining Kiss.
I'll have to save this one for another special team I'll think of. Can't wait to transfer my Gliscor though, he'll work well on my sandstorm team. Basically against special attackers, they'll be hard pressed to break through Sylveon. Physical attackers will tear Sylveon to shreds though.