Mirage Arena

The Mirage Arena is a new world introduced in Kingdom Hearts Birth by Sleep, specifically for the game's multiplayer mode, Joint Struggle. Its name could may refer to the fact that more than two of the same character can be used in the multiplayer mode that takes place here, since the word mirage comes from the French word "mirror", and seeing reflections or doubles is a common occurrence of a mirage.

Joint Struggle
In the Mirage Arena, a gameplay mode for up to three players known as Joint Struggle is held. Here, players can interact in the Lobby and later battle the Unversed cooperatively. Joint Struggle features unique abilities that cannot be used in other types of gameplay, and allows bonuses to be obtained for the game's single-player story mode.

Appearance
From its exterior appearance, the Mirage Arena appears similar to Space Paranoids. A central orb in the middle, several protrusions and large, strap-like objects surround it.

On the inside, the world has an appearance similar to a space station. In the Lobby, glowing neon steps highlight a dark floor. A wide window gives a view of space, and a Moogle stands in the corner running the Medal Shop. When you set records in the Arena's games, you can get medals and exchange them for rare items in the shop. Blue data screens are also displayed on the window. In the Battle Arena, red screens surround the players as they battle Unversed on a terrain colored varying shades of blue. The surrounding space can also be seen through the windows in this area. A third area, also used for battle, places players in a room with a dark floor and walls.