This is the spice for easily soloing the Serperior raid

Skill Swap on turn 1 to steal Contrary for yourself. Then just spam Overheat and Tera ASAP. On the turn that Serperior nullifies your ability and resets your stats, use a different Fire-type move to prevent your special attack from being lowered. Then spam Overheat again until you're at +6. And should you get hit by Gastro Acid at some point, just use any Fire-type move other than Overheat.