(ima doc player)
I dunno exactly how chaingrabbing works with Mario, but i'd imagine it works the same as with Doc.
If that's the case, then it's not bad to take Fox to FD, cause you can chaingrab the hell out of him w/o platforms to get in your way.
Beyond that, I like counterpicking corneria because I can stand on the fin and get good angles with my pills, because i can chaingrab left of the fin, and i can stand under the fin and walltech if i need to.
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I'd imagine Yoshi's Story would be a useful stage for mario, since you can use your up+b glitch and add some options to your recovery. Ya obviously wouldnt want to take marth or ganon there, though. You'd also wanna watchout for a bowser or DK on there, too. >.<
Um........
beyond that, I think you'd have to do more counterpicking against your opponent if you need to. But that's always a risk if you dont know who they can play.