High Priestess Bishium is one of the High Priests of Gorgom. She can discharge laser beams from her eyes. After losing her powers from the "Stone of Earth" within her to revive Shadow Moon, Bishium is reborn as Grand Mutant Bishium, a white-haired purple rhamphorhynchus, pterosaur-like creature. In this form, she still has her usually powers and she can spin around to create twisters. Bishium became overconfident of herself and even tried to convince Shadow Moon that her plans could finally defeat Kamen Rider Black, ignoring advices from her good allies, Darom and Baraom. When it came to the final confrontation with Black, she tried to get the King Stone from Kotaro by taking control of the mothers and capturing Kyoko. In the conflict, Bishium held Black so that Shadow Moon can shoot a beam that will rip out Kotaro's King Stone. It failed as Bishium is destroyed by that beam.