World 5, also known as World 5: Trial of the Galaxies, is the fifth world of Super Mario Galaxy 2. It is located in a galaxy cluster. This world holds seven galaxies, with the final galaxy being Bowser Jr.'s Boom Bunker, where Mario fights Bowser Jr. for the final time in the game. Bowser Jr. now fights using his Boomsday Machine. This world has a Warp Pipe after the Space Storm Galaxy, which will take Starship Mario to the other set of galaxies in this world when entered. The Warp Pipe can be entered by simply moving to it.
- Space Storm Galaxy
- Slipsand Galaxy
- Shiverburn Galaxy
- Boo Moon Galaxy
- Upside Dizzy Galaxy
- Fleet Glide Galaxy (this galaxy is unlocked when feeding Star Bits to a Hungry Luma on the map)
- Bowser Jr.'s Boom Bunker
- This is the only world where Yoshi does not appear in any galaxy.