After a battle, he transformed into a volcano and fought her again.

Momo chased him to the bottom, where he had possessed a fissure, and fought him. Cackling, he summoned all his ghosts back to him and retreated deep into an underwater trench. However, the Boss Ghost in fact survived being defeated by Momo, and fell into the ocean, crushing a sailboat as he went. An army of Ghosts arrived to help their leader but were all defeated and Momo used one last spell to strike lightning onto the Boss Ghost, causing his powers to be returned to the Spell Book and he fell out of the sky. Momo began to battle the Boss Ghost using spells while the Boss Ghost tried to eat her. But, the Boss read from the Spell Book and consumed its' powers, turning him into a massive three-eyed monster. The Boss was trying to escape with the book but Momo went on a broomstick and caught him. Momo fought her way through all of Boss Ghost's generals until she eventually caught up with him on top of the school's tower. Then, he summoned the other Ghosts to take over the school. When Momo and her friends were studying in the Magic Cat Academy library, the Boss appeared and grabbed the Spell Book.

Magic cat academy