Smogon Berserker Jean Mewtwo (BH)

Berserk Jean (Mewtwo-Mega-X) @ Mewtwonite Y
Ability: Simple
EVs: 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Quiver Dance
- Boomburst
- Stored Power
- Vacuum Wave

Apparently pokemon that have two mega can switch into the other as long as you have the opposite mega stone
Boomburst does a ton, as well as stored power. And mega evolving into Y wakes up anyone tryna put you to schleep with Y's insomnia