Mirage Island is an island on route 130 which only contain one pokemon, Wynaut! to see the island, first, go to the right house on pasifidlog (spelling?) and talk to an old man inside that house. but, the rumor said that Mirage Island cannot be seen, so it's very rare to see it... if you want more information to see this island, go to
http://www.serebii.net/games/mirage.shtml
hope this usefull...