Eye to Eye in the Secret Room
From the Super Mario Wiki
Eye to Eye in the Secret Room is the sixth mission of Big Boo's Haunt in Super Mario 64 and Super Mario 64 DS. In Super Mario 64, it is the final mission of the course, and in the DS version, this mission can only be completed with Luigi. The mission's objective is to defeat the Big Mr. I in a secret room on the third floor.
The player has to enter the far right room of the second floor and make their way to the door on the opposite side of the room, avoiding the Bookends and the tilting platform. Behind the door is a blue ! Block in the N64 version or a red ? Block in the DS version. The player has to grab the power-up from inside, jump up to the door above in the previous room, and enter the secret room behind the Boo portrait, all before the power-up wears off. Once inside the room, the player has to defeat the Big Mr. I by running around it until it shrinks and disappears. Once it does, the Power Star will appear.
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