Mega Charizard Y is a beast. My in-game set up is
Charizard @ CharizarditeY
Nature: Modest
EVs: 252 SPA/ 252 Speed/ 4HP
Hidden Power Ice
Solar Beam
Flamethrower
Air Slash
HP Ice is almost always a 1 hit kill on dragonite, garchomp, salmence. Mega Charizard Y doesn't get enough credit imo