Gameplay sum up: The game's hub is the Comet Observatory that leads off to the 6 galaxies in the form of domes. Each contain 5 levels, 3 of which contain 6 individual objectives; when they are completed, you will rewarded with "Grand Stars" (a total of 120) that will, in turn, begin to unlock more of these galaxies. The remaining two levels in each galaxy are stand-alone boss battles or single objective levels. After you collect the required amount of Grand Stars, you will face off with Bowser and save Princess Peach...yet again. The game's biggest addition is its spherical level design; think of yourself walking on the surface of a giant ball, where gravity pulls you to its surface, allowing you to traverse the area like it's flat; but as it's not, your perspective will shift depending on where you are on the sphere. After the brief training level, Mario is introduced to his new sidekick, Luma, a baby star. Luma imbues him with an ability to do a spin by shaking the Wiimote at any time during the game...

This ability has many uses, including spinning in the air, allowing you to reach higher areas; spinning into obstacles and breaking them to reveal coins and/or items; and you can also spin into enemies, resulting in them being stunned for a limited time. The game's stages play out like a mix of Super Mario 64, Super Mario Sunshine and even Super Mario World. Unique to this game is, of course, the spherical levels, and to traverse between them, you'll use Launch Stars. To use them, you'll jump up and swing the Wiimote up, resulting in you flying into space and landing on the level's next sphere. You will often have to reassemble Launch Stars by finding 5 Star Pieces, thus activating them for use and letting you progress to the next area. There are also Star Bits that can be seen falling all over every area, which you can collect by simply pointing at them, and then use them as currency in the main hub to unlock bonus levels, or as projectiles to temporarily stun weak enemies with the B-trigger.

There are also a few unique power-ups for Mario to obtain, including the ability to turn into a bee, giving him the power of flight in short spurts, along with the ability to climb on honeycomb walls—just watch out for the water, if you fall in, you'll lose your powers. In addition, a Fireball power-up gives him an ability to shoot fireballs that can light torches in a few levels and attack enemies. Other than the main levels, there are several side/bonus levels that use the Wiimote in particularly interesting (and fun) ways. One level has you ride on the back of a giant sting-ray like a surfboard down a water-filled race track while trying to avoid falling off the level's edge by steering with a tilt of the Wiimote left/right, accelerate by holding down the A button, and get air by flicking it back. This is just one example of bonus levels; there's many more throughout.