A soul room is a room existing within an individual's mind that contains items reflecting their personality. Shadi was able to access various characters soul rooms through use of the Millennium Key. While inside he was able to redecorate their room to change their personality and have them do his bidding. He was also able to destroy the room in order to kill the person. By redecorating the soul rooms of Yugi's friends, Shadi forced Dark Yugi into a series of tests.