Charizard-Mega-Y with return = viable?
*Stockpile and Swallow, not Spit Up.How about No Guard M-Mawile? "Its docile-looking face serves to lull its foe into letting down its guard." It has Dynamic Punch, Play Rough, Stone Edge, Mega Kick and the Elemental Fangs as moves that benefit from it. If it proves to be underwhelming, it could receive Megahorn, because it's jaws are modified horns. Or Zen Headbutt. Or both.
As for a defensive Mega, Prankster could work. It's probably the most fitting defensive ability (arguably Illusion is, since it's the Deceiver Pokemon and all, but that would be bad, and it doesn't actually shapeshift). It has Stockpile and Spit Up as somewhat recovery, plus Pain Split, Taunt, Stealth Rock, Swords Dance, Baton Pass, Toxic
and Swagger. Can't think of a move that would fit flavor-wise and more viable though, so it probably wouldn't get movepool additions. Maybe Spikes?
Name: Typing: Ability: Stats: Movepool Additions: OU / Uber: Justification: