Actually, if you want to do a really silly deck... Solgaleo GX/Camerupt EX. I got rolled by one once because he got off his GX attack and grabbed 4 Burning Energy.
I tried playing Mewtwo Y. I couldn't do it, which makes me incredibly sad. Now, I'm sitting on Zygarde Turbo. Yay for braindead decks! But yeah, I didn't expect the Solgaleo wombo in to Camerupt until he hit me for 250. Was not happy.