Pidgeot (M) @ Mega Stone
Ability: No Guard
EVs: 60 HP / 252 SAtk / 196 Spe
Modest Nature
- Sing
- Hurricane
- Boomburst
- Heat Wave
Save Sing for Chansey and start denting the opponent's team inch by inch. A Shell Smash set would be viable too, I guess. But with Diggersby and Mega Lopunny around, you'll never be able to pull that off.
Beedrill (M) @ Mega Stone
Ability: No Guard
EVs: 196 HP / 252 Atk / 60 Spe
Adamant Nature
- Coil
- Megahorn
- Gunk Shot
- Roost
While it's hopelessly walled by Steel Types, take them out of the equation and Mega Beedrill becomes a violent threat that can break down walls quicker than anything else can. It's Adaptability-boosted 120 Base STABs are nukes right off the bat. Coil is to fix the moves' accuracy and also providing enough bulk to Roost off and live longer. Watch out for Sableye though.
Lopunny (M) @ Mega Stone
Ability: Scrappy
EVs: 252 HP / 252 Atk / 4 Def
Adamant Nature
- Shell Smash
- Extreme Speed
- Hi Jump Kick
- Milk Drink/Recover
Well hello there, Sableye! The additional bulk is to survive Diggersby's Fake Out, while the Speed creep is also fixed by Shell Smash. Everyone is happy!