Grill O'Wisp

His signature and the best choice at S5: HP%, unconditional Fire DMG and CRIT Rate on HP loss, with near full uptime since he burns HP constantly. At S1 it is still good, ranking just behind Wrathful Vajra. During Stun, briefly hold Return to Ashes - Sacrifice between Chain Attacks to refresh the buff.

The Fire DMG is wasted, but it has an HP% main stat and even more CRIT Rate than her signature. The 5s buff is refreshed constantly by charging, though some combos need an extra HP drain to keep it up.

Its value comes from HP% and an unconditional +15% Fire DMG. The CRIT Rate bonus on HP loss is nearly useless, since Banyue only drains his own HP once before combat.

Most of its value comes from the HP% main stat. Its CRIT Rate needs Billy to lose HP. You can force that with Drive Suppression before each EX, but it slows your combos and makes HP harder to manage, so it's not recommended for most players.