Power Moon

Power Moons are collectible items in Super Mario Odyssey. Equivalent to the Power Stars in Super Mario 64 (and its remake), Super Mario Galaxy, and Super Mario Galaxy 2 and Shine Sprites in Super Mario Sunshine, they can be found in the various kingdoms of the game and used to power the Odyssey in order to let Mario reach additional kingdoms. Collecting 250 Power Moons unlocks the Dark Side, while collecting 500 Power Moons unlocks the Darker Side. Collecting 880 Power Moons, not counting the additional ones that can be bought at Crazy Cap after completing the main story will turn the Odyssey's sail into a golden color, and unlocks a painting in the Wedding Hall at Honeylune Ridge that allows players to play through a harder version of the final battle with Bowser. Collecting 5 Moon Shards yields a Power Moon as well.

Gameplay-wise, they act mostly like the Power Stars and Shine Sprites in earlier titles, being the main collectible Mario needs to find to progress. Unlike these however, there are between 1 and 104 per kingdom, and completing them does not cause Mario to exit the stage unlike in several prior 3D Mario titles.

Larger variants called Multi Moons also exist in the game. These count as three Power Moons in one, and can be attained by defeating bosses or clearing main story missions.

Including the three-moon count from Multi Moons and post-game store moons, there are a total of 999 Power Moons available in the game.

Colors
Power Moons feature a different color depending on the kingdom in which they are found. Their color also matches the color of the pole of the Kingdom's Checkpoint Flag.

Trivia

 * When Mario collects his first Power Star in the Mushroom Kingdom, Cappy says that he didn't know that Power Moons come in different shapes. This suggests that Power Moons and Power Stars are different shapes of the same object, a distinction that may also include Shine Sprites.
 * Yellow Power Moons are the only color of Power Moons that can be found in multiple kingdoms.