Mega Mawile, no questions asked
It's bulky enough to use both Swords Dance and Substitute.
It has great attack already, plus it has Huge Power
Look at this Calc
>+2 252+ Atk Huge Power Mega Mawile Focus Punch vs. 252 HP / 252+ Def Shuckle: 238-280 (97.5 - 114.7%) -- 81.3% chance to OHKO
Shuckle can be destroyed by this.
Trait: Intimidate --> Huge Power
EVs: 252 Hp, 252 Atk, 4 SpD
- Swords Dance
- Focus Punch
- Sucker Punch
Sucker Punch is to hit Ghost types immune to Focus Punch
Hope I helped!