Starship Mario is a Mario head-shaped planet and space craft in Super Mario Galaxy 2 used to travel across the universe. Although notably smaller than the previous games' hub areas, it serves as the hub of the game and has, more or less, replaced the Comet Observatory from the first game. Other than its smaller size, another difference from the Observatory is that it also has changing backgrounds, the appearance of which depend on the world that it is currently in.
While on the ship, Mario is able to explore and interact with various non-playable characters, including Lubba and the Co-Star Luma. Some other characters in the game appear after certain Stars are collected or a specific goal is met.
Much like Delfino Plaza from Super Mario Sunshine, Mario can ride Yoshi here. The egg which contains him is located on the 'nose' of the ship, after rescuing Yoshi in Yoshi Star Galaxy. There is also a room under the area with the pressure switch which can only be accessed by jumping into a large chimney which leads into the room, or by going through a secret door in the bill of the ship's 'cap'. The room contains a large ball of light similar to the beacon in the Comet Observatory, a telescope and some books. There are also several platforms at the edge of the room which can become display cases. Various power-ups, such as the Fire Flower and Rock Mushroom, begin to appear on display after they are used to obtain certain Power Stars. However, the display cases cannot be penetrated and thus the power-ups inside cannot be used. The Cloud Flower, one of the appearing power-ups, is the only power-up that can be used on the ship. The Toad Brigade's ship also stays close to the ship. Transfer between the two ships is possible via a Warp Pad.
After Mario collects the first Power Star in the Sky Station Galaxy, he lands on a starship. This is Starship Mario, captained at first by Lubba, a purple Luma. But when Lubba learns of Mario's mission to save Peach, Lubba turns the ship over to Mario and refashions it in the shape of Mario's head. Starship Mario acts as the hub world. From this ship, Mario can blast off for new worlds or launch re-exploration missions to previously visited galaxies.
The ship's main purpose, though, is to allow Mario to travel between and select galaxies to visit. To leave the ship and go to the world map, one must step up to a ship's wheel near the top, in front of which is a small weight-activated button. When pressed, the button sends the player to the world map, from where he/she can select galaxies.
The Engine Room on Starship Mario doubles as a trophy room of sorts. As Mario explores the cosmos and finds new power-ups like the Rock Mushroom and Spin Drill, they are stored in this room. Mario cannot take these items out of the Engine Room, but he can view them at any time.
As Mario encounters citizens of the cosmos, some choose to travel on Starship Mario. The Star Bunny, Whittle, Gearmo, Bob-omb Buddy, and more take up residence around the ship and are happy to chat whenever Mario has a free moment. While making the rounds of chatting, be sure to play with any available Chance Cubes or pick up freebie Star Bits.
Below is a full list of the characters that make an appearance on the Starship Mario.
Starship Mario can also be seen on the newest Super Mario Galaxy stage in Super Smash Bros. 3DS/Wii U.