Memento's Tough Enemy Ose's Gimmick

It retreats once HP drops below 〇〇%. So I thought I could one-shot it and tried with Reason, but as expected, I couldn't ignore the gimmick. Well, HARD has Ose & Decarabia, so it was impossible either way (lol). I was definitely too lazy 🫠 By the way, both have fire resistance, but I removed it with Orobas's Fire Guard Break.