If you manage to get 2 Swords Dance with a Technitian Scizor (252 EV in Atk and Adamant nature is recommended), you OHKO Shadow Mewtwo, Armored Tyranitar, Kyurem-B and Mega Flygon with Bullet Punch (don’t worry about speed, it’s priority). Then, you can OHKO his D.Haxorus with Superpower and D.Volcarona can be serverly weakened with Bug Bite or dealth with teammates. In the best case, a Mold Breaker user with Earthquake like Excadrill or Haxorus. Other strong physical Wallbreaker (Mega Kangaskan, Mega Medicham, Conkeldurr or Lucario being immunes to Sludge Wave and resident to Dark Pulse+Giga Drain) do the job very well.
Mewtwo, Kyurem-B, Mega Flygon and Tyranitar (if he use Dragon Dance since it is not an OHKO) get destroyed by a Choice Scarf Gardevoir using Moonblast.
I have a good record at destroying Reukra in Hard mode. If you ever need team advices, ask me.