Metroid Fusion released on Game Boy Advance the same day as Metroid Prime for the Nintendo GameCube. After an eight year hiatus, the series was both reinvented as a first-person action game and continued in its traditional 2D format in Fusion.
Super Metroid leaves Samus alone once again. During the battle with Mother Brain, the Metroid hatchling was killed and Samus escapes the planet just before it self-destructs. Fusion begins as Samus investigates the planet SR388, home to the Metroid, and unknowingly becomes infected with X Parasite virus. The X Parasite become one of the game’s main antagonists, although they are quite different than we are used to. These parasite infiltrate the host’s nervous system and strip it down from the inside, killing it and taking over the husk of a body. The Galactic Federation recovers Samus’ body after her ship crashes and they discover that Samus has indeed been infected.
In order to save Samus, scientists use leftover cell tissue from the Metroid hatchling and infuse Samus’ DNA with that of the Metroid. As the Metroid were the X Parasite’s main enemy on the planet, the DNA now in Samus helped to rid of the virus and save her. However, it created two new interesting circumstances for the Metroid storyline.
Samus now has Metroid DNA, making her weak to the same weaknesses that the Metroids had. The X Parasite that were living inside of Samus now inhabit Samus’ old suit. So, with Samus running around with a new fancy suit, she is being hunted by a ghost of herself that carries the exact weapons needed to kill her quickly. It adds a new sense of dread to the player.
While Metroid Fusion follows the traditional 2D style of Metroid game, it breaks some of its conventions. It does have an open map and encourages free exploration, gating certain areas until the player receives a particular powerup. However, Fusion numbers the areas that the player must visit. A navigation system and a narrator help to guide the player along, rather than encouraging the standard wander that players had been known to perform in other games.
What remains impressive is that this type of game was debuting on a handheld console. Game Boy Advance generally was impressive as it felt like a SNES in your pocket, but here in particular we were able to take the big adventure anywhere with us. Fusion too, paired with the aforementioned Metroid Prime, allowing the player to obtain a Fusion suit in the GameCube game and to unlock an emulated version of the NES classic on GBA. The latter was too particularly impressive, as it was still before the likes of Virtual Console and even Nintendo’s own NES Classics revival series of cartridges that would soon grace the console.
At the time of this writing, Metroid Fusion is the last in the Metroid timeline. There was another game that was revealed (kind of) and later cancelled. However, Metroid Dread has long been out of the cycle for production as far as we know. The end of Metroid Fusion certainly leaves Samus in an interesting place and could make for a new type of game if Nintendo decided to incorporate more of the mutation of Samus into the storyline.