At some point, Krell learned of the Ultragem's whereabouts in Castle Grimm and prepared to visit the building, gaining prior knowledge of the gem's guardian, Serpentus. After battling her way through immense dangers, she was eventually bested by Serpentus, twisting her ankle when the snake burst from the ground. Krell was rescued by Amy Rose and Tekno the Canary, the girls assuming that was why they had arrived there. An injured Krell convinced Amy to find the Ultragem for her. However, upon her success, Krell ignored Amy's recent danger, instead rummaging through Amy's backpack to retrieve the gem. Getting her hands on it, she unveiled her true, villainous plans.
Unhappy that Amy had called her dialogue "corny", Krell used Ultragem to plunge Amy into a pit of quicksand, although she was rescued by Tekno. She then got her revenge on Serpentus by turning him into mist. After a suggestion from Amy to turn the castle into solid silver, Krell did so, before once again being insulted by her foe. Angered, Krell aimed to turn the heroes into mist, but missed them. The blast rebounded off the polished walls and turned her (and the Ultragem) into dust.
- Xenor's name is a pun on "Xena: Warrior Princess", with her look being rather similar.
- Krell's pigtails suddenly come undone when she grabs the Ultragem.