Boo in a Box

Boo in a Box is the hidden sixth mission of Deep Dark Galaxy in Super Mario Galaxy. This mission can be done during any standard mission.

Layout
The player must make their way to the bottom of the underwater cave and find a Green Shell. Launching the Green Shell at one of the mines surrounding the broken ship mast will cause them all to explode, revealing a Launch Star. The Launch Star will send the player inside of a floating box with a single Atomic Boo and a Ground Urchin inside. Flipping the arrow to change gravity until the player is on the wall to the right, the player will find a crystal blocking a hole. Shattering the crystal will let in light and the player then has to lure the Atomic Boo into the light, causing it to be defeated and dropping the Power Star.