Originally, when Mickey first meets him in his dream, he was shown to be friendly at first when he invites him into the mirror. Then later, he turns out to be greedy and evil, and would pick on Mickey, tease and play tricks on him whenever he entered a room or visited a new area. Toward the end of the game, he reforms, his personality changes and it was revealed why he invited Mickey into the mirror was because he only wanted a friend to play with. He then becomes kind and friendly when Mickey invites him to come home with him to his room and out of the mirror.
In the game, he invites Mickey Mouse to come inside the mirror to go exploring. When Mickey goes to the next room and finds the mirror that leads back home, the Ghost appears on the other side and scares Mickey. He then uses his electrical powers to destroy all the glass in the mirror and prevented Mickey from escaping. He then spreads all the glass pieces through all the areas and rooms inside the mirror, where it was up to Mickey to find all of them. At times, he would play tricks on Mickey or just scare him. He reforms in the end when Mickey invites him to come home with him to his room, and later on, he becomes good friends with Mickey.
But if the player doesn't collect all the pieces and only finds 8 pieces, the Ghost won't be able to go home with him.