The Secret of Buoy Base

The Secret of Buoy Base is the second mission of the Buoy Base Galaxy in Super Mario Galaxy. Its Power Star is one of three Green Power Stars in the game.

Layout
When Mario initially dives into the surrounding pool of water, he can find a caged green pipe and open it by luring one of the Torpedo Teds into it. The pipe takes Mario to the outside of the planet, where Mario must lure Bullet Bills into a cage that contains the Green Power Star. Falling off the platforms underneath the planet results in Mario ending up back in Buoy Base's water pool.

Trivia

 * If Mario falls into the water after he has used the hidden Warp Pipe, gravity prevents him from retracing his steps, and he has to use the Warp Pipe to get back again.