Zard-Y really nice paired with Hippo with some HP invested on it, Metagross without priority may seem odd but better imo to have another burst move also faking out your opponent vs priority.
Hippowdon @ Leftovers Ability: Sand Stream Level: 50 EVs: 32 HP / 19 Def / 15 SpD Impish Nature - Stealth Rock - Earthquake - Yawn - Slack Off
Primarina @ Mystic Water Ability: Torrent Level: 50 EVs: 26 HP / 32 SpA / 8 Spe Modest Nature - Moonblast - Sparkling Aria - Aqua Jet - Flip Turn
Metagross-Mega @ Metagrossite Ability: Tough Claws Level: 50 EVs: 32 Atk / 2 SpD / 32 Spe Jolly Nature - Meteor Mash - Psychic Fangs - Ice Punch - Earthquake
Hydreigon @ Choice Scarf Ability: Levitate Level: 50 Shiny: Yes EVs: 2 HP / 32 SpA / 32 Spe Modest Nature - Draco Meteor - Dark Pulse - U-turn - Flamethrower
Mimikyu @ Life Orb Ability: Disguise Level: 50 EVs: 2 HP / 32 Atk / 32 Spe Adamant Nature - Swords Dance - Play Rough - Shadow Sneak - Shadow Claw
Charizard-Mega-Y @ Charizardite Y Ability: Drought Level: 50 EVs: 14 HP / 20 SpA / 32 Spe Timid Nature - Flamethrower - Overheat - Solar Beam - Roost