Quick post, but yes on Yawn. Forcing an opponent to choose between sleep and shuffling is a great momentum move. Also a definite no on Spore, this move is just far to overpowered for us to throw around, especially onto a Pokemon that is already so great.
Something that I think warrants significant discussion is Roost. Prankster recovery is an extremely effective tool, as anyone who has used Murkrow in LC (or even OU) or Sableye in DW can attest to, and this is with very relatively frail and offensively weak Pokemon (though complemented with FeatherDance or WoW). Of course, recovery is very important for this Pokemon (at least imo) so I'd lean towards Allowed (or maybe just Recover?) Of course, we could also make Roost illegal with Prankster, though that's pretty convoluted.
tl;dr don't underestimate the power/utility of Prankster Roost - it is very good
Edit: I think Wish is definitely a good idea though. Gives you something to do in free turns given by Sub/Encore/Whatever other than attack and gains an insignificant boost from Prankster. Also, why is Light Screen disallowed? Helps beat counters too easily?