252 HP / 252 Atk / 4 Def
- Stone Edge
- Drain Punch
- Stealth Rock
A +2 Earthquake from Altaria does pitiful damage to Regirock, while Regirock threatens to 2HKO Altaria with a stab Stone Edge (with stealth rock damage). Even if Altaria chooses to attack with +2 Dragon Claw, the result will be the same iirc. Altaria can keep using Roost but it's downfall would be inevitable. lol
I hope I got this right, and that my calcs were actually correct. If not, feel free to correct me!