Charizard-Mega-Y @ Charizardite Y
Ability: Drought
EVs: 252 SpA/ 4 SpD/ 252 Spe
Timid Nature
IVs: 0 Attack
-Fire Blast / Flamethrower
-Solar Beam
-Focus Blast
-Roost / Defog
Mega Charizard Y provides coverage against Water and Ground type Pokémon with Solar Beam, which only takes one turn to charge because of its ability Drought. Fire Blast 2HKOs most Pokémon, including Mega Gardevoir, opposing Charizard and Latios. You could also use Flamethrower over Fire Blast, but it's a severely weaker STAB and it can't 2HKO most of the metagame. Focus Blast 2HKOs defensive Tyrannitars and Heatrans, and Roost keeps Mega Charizard Y alive to sweep another team. In conjunction with Infernape, Mega Charizard Y can clear most of Infernape's weaknesses, such as Water and Ground types with Solar Beam, 2HKO most Flying types with Fire Blast, and Focus Blast the remaining. Extreme Speed users and bulky Psychic types may still hurt, and entry hazards too. You could replace Roost with Defog to clear entry hazards for Infernape. Toxic and Thunder Wave are also problems, as they lower the HP of both Mega Charizard Y and Infernape, limiting their usefulness as wallbreakers and chip damage.