Moon

The Moon first appeared as a playable area in Super Mario Land 2: 6 Golden Coins, in which it was one half of Space Zone. It was populated by many pigs.

In Paper Mario: The Thousand-Year Door, this is where the X-Naut Fortress is located. It can only be accessed via a cannon at Fahr Outpost or the Teleporter located in Rogueport Sewers. According to Goombella, a Goomba landed on the Moon in '69.

Many confuse this with the tiny moon in World 5-8 of Super Mario World 2: Yoshi's Island.

In Mario & Luigi: Superstar Saga there is a god called the Thunder God and his head is shaped like a moon.

The moon appears in many Mario Party games. Twila a character from Mario Party 6 is also a moon.