Grab the ledge vs Roy = gg.
Here are pretty much most options from the ledge.
Keep invincibility on ledge, let go and jump back on.
Ledgehop uair
Ledgehop jab
Ledgehop Ftilt (Remember the angles too sometimes)
Ledgehop then jump to uair (If you predict an attack from above)
Ledgehop, then jump Dair (Predicting an horizontal attack if they are stupid)
Ledgehop, delay down-B. (If he went for a grab there, the grab will whiff and it will generally send him off-stage reversed. lol... though I normally do this on reaction.)
RLD, go back to the edge again, refresh invincibility, WD in or RLD again idk.. lol.. roll.. jump to the platform with more WDs. (Those mixups are without moves, it's just to make you gain center again and avoid attacks.) Look where he is and look how he can cut you down, you have to predict where he's going.. make him miss.
RLD Fair, Dair.
WD in Jab, ftilt, uair, Dair.. again depending on positioning.
WD in to roll goes VERY far into the stage.. I generally do this when he already committed an attack close to the ledge.
WD in Bair if he overcommitted
WD in Side-B
It's really hard to explain how to predict or react to the opponent but that's basically your options.