I think finding a way to punish it for staying on the field to long might work, something like Poison, Leech Seed, especially Burn may help you chip it down. Also strong Electric, Psychic, Flying and Fairy type moves would be useful, maybe something like a Talonflame 32+ Sharp Beak Brave Bird? Or Mega Floette, it resists Close Combat and can probably OHKO it with Light Of Ruin or something, and Mega Gardevoir 4x resists Close Combat so it could probably deal with it okay. Also, Grimmsnarl could use Swagger to give the Staraptor -2 and confuse it? I think a Zap Cannon from Raichu-Y would probably OHKO it? I'm not entirely sure, because the Regulation is so new, so this is a bit like a braindump XD. Hope this helped