Sceptile is a hard one to completely counter, especially special sets. Pokés like roselia can switch in and resist special based hits and retaliate with sludge bomb. But roselia fears acrobatics. Alraria is good too but cant take a +2 Rockslide or Hp ice. Sap sippers like boufallant are good but can be KOed by focus blast. Charizard, Moltres, and flareon are good but all of them still are beaten by that rockslide. You must know its moveset to counter it. Scout out the moves with a Pokemon like rotom-c. Then choose its best counter.