My mario 64 fever dream included a secret corridor that had a lot of courses (40 Courses total) It also had a star door at the end of the corridor which led to a room where you could talk to this goomba and he would grant you the ability to play as a koopa troopa. When I unlocked the koopa troopa, I could actually slide under secret areas to access secret parts of the castle. I also played some of the courses in the secret corridor.

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