Metroid Prime 2: Echoes is a first person action-adventure video game developed by Retro Studios and published by Nintendo for the GameCube video game console. It is the seventh published game in the Metroid series, a sequel to Metroid Prime, and the first game in the series with a multiplayer feature. Echoes was released in North America, Europe, and Australia in 2004; and in Japan under the name Metroid Prime 2: Dark Echoes in May 2005. The story of Echoes follows bounty hunter Samus Aran after she is sent to rescue Galactic Federation Marines from a ship near Aether, a planet inhabited by a race known as the Luminoth. There, she discovers that the troops were slaughtered by the Ing, a race that came from an alternate dimension of Aether. Samus must travel to three temples to ensure the destruction of the Ing, while battling Space Pirates and her mysterious doppelgänger called Dark Samus. Retro decided to make the game different from its predecessor by adding more focus on storyline and including new gameplay elements. Nintendo launched a viral marketing campaign to promote the game that included several websites written as if taking place in the Metroid universe. Echoes' single player mode and graphics were praised by critics, while its steep difficulty level and multiplayer components were met less positively. Since its release, Echoes has received several video game industry awards, as well as spots on "top games" lists by Nintendo Power and IGN. Over 800,000 copies of the game were sold worldwide. In 2009, an enhanced version was released for Wii as a standalone game in Japan and as part of Metroid Prime: Trilogy internationally.