Master the Pivot and Roy's Fsmash becomes something worthy of the Gods. That's most of my play. I can Fthrow Link, Samus, Ness, Mewtwo, Falco, Fox, Falcon, etc. in a chain throw for the first two and then run, pivot to Fsmash. It is beautiful. DDing on your opponents whim and immediately Fsmashing is great as well. Roy's Dair is also his money move because when sweet spotted it has more knock back then all of his aerials and if you master his dair you can send the sweet spot in any direction. I can use Dair instead of any of Roy's aerials and juggle with it. BUT the landing lag on his Dair if not done correctly is punishable. I recommend lots of practice with Roy. And being able to wavedash in and out of your opponents pressure while using dtilt is incredibly useful. Right when the dtilt is on dash to pivot fsmash. No one likes my Roy lol because his Fsmash which isn't easily comboed becomes childs play to use with the pivot, when Fair sends them what would usually be out of reach is nothing to worry about with pivot fsmash. PIVOT FSMASH FTW! lol
AND should I even have to bring up his counter, and my favorite is Uthrowing and using Usmash right away to miss, so the opponent thinks they can get me on a whim or pressure me, but its just enough time to 'whoops' COUNTER! game set!