Wait, what? There isn't a special double dance set already on here?
Gen 8 RU
Cobalion @ Leftovers(I'm not sure about Leftovers, suggestions are welcome)
Ability: Justified
EVs: 252 SpA / 4 Def / 252 Spe
Timid / Modest Nature
IVs: 0 Atk
- Calm Mind
- Flash Cannon
- Rock Polish
- Focus Blast
Well, Leftovers is healing, Justified is its only ability, and is useful when you switch into a dark type move not named Knock Off, the EVs are your bread and butter sweeper EVs, Timid helps with revenge killers, Modest is more power, 0 IVs minimize Foul Play damage, Calm Mind patches your bad SpD and raises its mediocre SpA, Flash Cannon is STAB, and Rock Polish boosts speed, making it harder to revenge kill.
Other options: You could forgo Rock Polish for Taunt, Thunder Wave, or Stealth Rock if you want more support for your team. You could use Steel Beam, but with only Leftovers healing, it isn't the best idea. Air Slash could replace one of the STAB moves or Rock Polish. You could use Iron Defense, but that makes it almost complete Taunt bait. Volt Switch could be used to pivot out of bad matchups, replacing one of the STAB moves or Rock Polish. Alternatively, you could run a more defensive RestTalk set, but RestTalk can make it set up bait, or you could get unlucky with Sleep Talk. You could also use Substitute to stall time to set up Calm Minds, replacing Rock Polish.
Checks and counters: Revenge Killers: Physical Revenge Killers can outspeed and kill it. However, special Revenge Killers will have a hard time breaking past it if they don't have a super effective move or you haven't set up enough Calm Minds. I'm not sure what else would counter this, I'll put more later when I find more checks and counters.