Medusa · Holy Innocents' Cemetery

Go to Serpents' Lair in Holy Innocents' Cemetery. You do not need to obtain Joan’s Infernal Pyre first to claim this battle’s rewards. As soon as you see the gaze windup, stop attacking, turn your back to Medusa, and keep it turned until this gaze phase ends. Simply moving backward while still facing the main body is not enough; do not try to force through the gaze with a dash or parry either. Only after the gaze ends and recovery begins should you turn around, approach, and make a brief attack; keep watching the tail and melee windups; do not turn back early just to squeeze in another hit. Complete the post-battle story sequence and absorb the reward orb to obtain Petrifying Gaze and The Prophetess's Key; then open the weapon chest that appears to claim Rusted Harpè and Aegis.