Super Speed also true combos into U-air and U-smash at %s where those moves kill.
It's very important to know what Palutena can do with SS. It may look linear, but
it gives her access to a wealth of options. She can jump out of it allowing her to zip across the screen with an aerial or JC U-smash, she can Dash Attack out of it, she can grab out of it, she can use the momentum gained from it to wavebounce Auto Retical/Explosive Flame, if she initiates it in the air she can cancel the momentum from it completely and stop on a dime with no lag whatsoever (SS has a hitbox at startup so she can use this as a pressure/mix-up tool and if it hits she can combo into U-smash or any of her aerials), among other things.
It's basically a Spin Dash that trades raw damage for extreme flexibility. Because of this, don't expect a good Palutena to get predictable with SS. Shielding is safe against a decent chunk of these options (you won't be punishing anything tho; SS is safe on block because of how fast it is), but she can still grab out of it and that could lead to a stock even at mid-%s. Your response to SS should be as unpredictable and varied as the move itself. Don't respond to it a certain way every time or you'll get blown up.
I dunno about that, optimally spaced B-airs seem to be safe on block against Mario. I rarely get grabbed, jabbed, U-smashed, etc. OoS by Mario and when I do it's obvious that it's because I messed up the spacing. I've also never had a problem with Mario ducking under my F-airs. That shouldn't be possible seeing as Jigglypuff can't even crouch under it (same goes for B-air).
Anyways, that's my two cents. I would actually talk about the matchup and stuff, but the only Mario main I know has like the world's worst connection so I don't have a lot of good experience in it.