Most of that stuff I knew especially his horrid moves (tho disagree with bair) but the thing with back slash sounds hilarious.
Well, it's more of a quirk about me. Most Bairs kills, but Shulk's range for it is insane... If he can land it, it's going to hurt.
The Back Slash thing I found out after a Shulk used Back Slash instead of Air Slash to recover which lead me getting meteored, but Falco's second jump and Fire Bird allowed me to get back on stage. Ike's Aether, on the other hand was weird. I think the guy recovered, grabbed the ledge, and the second hit registered leading me to get meteored.
Anyway, Shulk's Uair is a good anti-air tool due because it's fairly fast and because of its vertical range. Like most Uairs, he can juggle with it at lower percents and because of its range. I don't really know what Ftilt is used for aside from spacing and killing at higher percents. Same thing with Dtilt except I don't know when it kills.
Down Smash is a good punish tool because it lasts so long, but it gets easily punished too because of its start up and end lag. Up and Side Smash seem like read and punish moves. Hmm, all his Smashes are good for roll, spot-dodge, and maybe air dodge punishes.
Uair, Bair, and Dair are all commit moves as far as I know and Shulks might not use them unless they're going for the kill.
Vision is weird in a sense you can nick it and it'll send Shulk somewhere else or if it hits, it'll do fair damage or kill. Air Slash is like ZSS's Boost Kick.
Most Shulks I've fought start with Buster or Jump, but I've heard good that Speed is a good option as well. A Shulk will either switch to Jump or Smash for kills depending on if they want an easier time killing in the air and off-stage or if they want to kill on-stage and reliably.
I don't know, I think Shulk's a versatile character, but like pretty much half or two thirds of the cast, there aren't a lot of Shulk players that I know of.