You'd probably get a bit more information on Roy posting in his relavent section, but I do believe our resident sugoi tactician Raziek has been working on Roy.
I'll list off whatever I can say, hopefully something will be of use!
Raziek made a helpful guide on stages, but suffice it to say, his best are Battlefield, Lylat Cruise, and Delfino.
Here's a link to said guide,
http://smashboards.com/guides/survey-the-battlefield-robin-stage-tactics.147/
As for Robin's best matchups, characters who have no projectiles/no way of dealing with zoning will be hit the hardest, these are mostly larger characters such Dk, Bowser, Ganondorf etc. However the unique property of Thoron is that it goes straight through nearly any projectile, so even against characters who have projectiles Robin can gain a good advantage, examples being Link, possibly Luigi, and Mario.
Robin's worst matchups are against rush down characters, most of Robin's moves are slow to come out, even his tilts. I've heard people say that Robin's worst matchup is against Little Mac....a good Little Mac
. His small stature allows him to almost always avoid arcfire when dashing and his close up game can't be beat.
From my experience playing Robin, people will try to shield Arcfire a lot, obviously, as it's a very powerful move. You're going to want to use it as unpredictably as possible, or in areas where they can't avoid it, for instance when they're landing on the ground. People will often panic at the sight of a stored Thoron, playing very defensively while waiting for you to deploy it. The best course of action for this is to wait a while before using it, or as with Arcfire use it in a position where they won't be able to avoid it, I.E. landing.
That's all I can think of right now, if I think of anything/find anything else i'll make sure to leave another reply!
