The Deep Dark Galaxy is a galaxy in the game Super Mario Galaxy. It features an underwater cavern. In order to unlock this galaxy, Mario must get 46 Power Stars. The Toad Brigade and the Starshroom appear in this galaxy.
The Underground Ghost Ship
Mario must battle Kamella.
Mario must run across several planets using bubbles as transportation.
Guppy and the Underground Lake
Mario must race Guppy.
Ghost Ship Daredevil Run (Daredevil Comet in Orbit)
This mission is only accessible, unless already completed, if a Daredevil Comet is in orbit.
Plunder the Purple Coins (Purple Comet in Orbit)
Boo in a Box
In the Bubble Blastoff level, Mario must dive to the bottom of the underground lake and fire a shell at the bombs surrounding the back of the sunken ship. A star will appear to transport you to a big box where you must alter gravity to make a light to kill the Boo that has the Power Star.
- This galaxy is similarly named to an area in the SNES game, EarthBound, called the Deep Darkness. A similar situation applies to the Dusty Dune Galaxy.
- The Underground room, accessible via a warp pipe at the top of the main planet is viewable from the beach. This is easier to view on the third star, as the cannon is missing. Standing where the cannon once was, looking just right of the smaller version of the starting planet, there will be a weird box like object at a very far distance. Flying there via hacking reveals the object to actually be the room the player needs a warp pipe to access, but the purple background is only viewable when Mario or Luigi is really close to the room encircling the room as a sphere. There is no way this room could be the Boo Box, as the Boo Box can be seen close to the planet from an area in the 2nd mission. It's revealed that all galaxies with a underground room have this kind of planet in the sky, with some more well hidden then others.
- For unknown reasons, there is a Launch Star high above the galaxy. It's unknown why it's there (it was probably there from early development they just forgot to remove it). It is only possible to get to the launch star by hacking and it will only shoot Mario or Luigi out into space with nothing to land on. This will make them fall to their death. When the level reloads, they will start out in space and die right afterwards which eventually leads to a game over. The only way to stop this is to press the Home Menu button and reset the game.
- Mario/Luigi can reach the Underground Ghost Ship quicker than they should directly by firing the cannon above the rocks. It is also possible in Bubble Blastoff. If Mario/Luigi reaches the area in Bubble Blastoff, they will be permanently be trapped there, as Kamella will never appear. Even if Mario/Luigi dies there, he will still respawn in the Ghost ship area. This can be fixed by quitting the level.
- The outside music for this galaxy is a remix of the Super Mario Bros. underground theme. This also plays when Dino Piranha/Fiery Dino Piranha's egg is cracked and at the start of the Ghostly Galaxy.
- It is possible to beat "Bubble Blastoff" without defeating the Undergrunt Gunner. This can be done by Wall Jumping on to a ledge in the cave behind the torches.