Mirage Island can be seen by the player when the personality value of one of the Pokémon of the player's team matches the random number between 0 and 65535 which is generated by the game every day. A man in one of the houses in Pacifidlog Town alerts the player as to whether or not Mirage Island can be seen and if the player can go there.
Wynaut ranging from Levels 5 to 50 are the only inhabitants of Mirage Island. The rare Liechi Berry can also be found in plantations on this island.
In the Pokémon Adventures manga, Ruby and Sapphire trained on Mirage Island along with Juan, Tate, and Liza. According to Juan, time in Mirage Island does not flow in accordance with the outside world, and carries a sun-dial on his person so he can actively estimate how long they have been on the island.