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Sleepy Boos are medium-sized Boos that Mario encounters in Hotel Delfino in Super Mario Sunshine. Sleepy Boos mainly appear in the hotel's attic, although one is located on the second floor of the hotel blocking the passage between two rooms. Sleepy Boos only appear in the Mysterious Hotel Delfino episode.
Sleepy Boos cannot be passed or jumped over; even F.L.U.D.D. does not affect them. Even though they are sleeping, contact with them will hurt Mario. The only way to defeat a Sleepy Boo is for Yoshi to eat it, thus clearing the way.
If Mario is riding on Yoshi's back and accidentally runs into a Sleepy Boo, he gets flung off the Yoshi, but if he attempts to get back on the Yoshi, he still gets flung off. It is very hard to mount on the Yoshi again after he runs into a Sleepy Boo.
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