Using regular Abomasnow with an Icy Rock might be better than using Mega Abomasnow. You get longer-lasting Hail and it frees up your mega slot for something else. The hail is mainly what you're using it for, right? It should also still be slow enough to make use of Trick Room, and MegaMence/Garchomp/Lando-T still get annihilated by Blizzards anyway.
IDK how well they would work out, but Whimiscott and (Mega) Audino are 2 other Trick Room setters that aren't weak to Dark or Ghost. Also, Psyshock > Psychic on Gardevoir so it's not walled by specially bulky pokes.
Quash kinda sounds useless on a Trick Room Team to me. You're going to be going first most of the time anyway, so having a move that makes Pokemon go last when they're already going last is kinda.....
Yeah, anything caught or bred in Gen 6 can be used in VGC, except for the usual banned legendaries. They call it the Pentagon rule because all Pokemon caught or born on a Gen VI game have a little blue pentagon on their status screen.
Oh thank you about that Pentagon Rule answer! :D Now I really have to think of more possible threats.
I can understand the thing you said about Quash. I put it there just to make sure there's an option for me to go first outside of Trick Room. The Psyshock/Psychic thing though, I chose Psychic to punch through physically defensive threats, which I think would be more common than specially defensive ones (I could be wrong about this though), but with that said, I'll take Psyshock now.
As for the Mega Abomasnow, I'm really partial about using the Mega, since it can set-up weather twice without any switch-outs, threatens Dragons and the Genie Trio well, and the sheer power of its Blizzards compared to an Icy Rock Abomasnow. Whimsicott and Mega Audino seem sketchy to me, since Whimsicott would be sharing various weaknesses with Abomasnow, and Mega Audino is underwhelming for an offensive strategy like Trick Room to say the least (as far as I know).
Thank you for the suggestions, I'll think about them! :D