- Fan Nickname:
- The nigh-unskippable Missile Tank in Sector 3, making a 0% run almost impossible, is nicknamed "Bob".
- The Xenomorph Xerox creatures found in the Main Deck and Sector 1 have no official English name, but they are commonly called "Genesis" by fans as a Romanization of their Japanese name.
- The orange suit Samus gets upon absorbing the SA-X has no official name, but it's usually called the "Omega Suit" due to it being an 11th-Hour Superpower and due to it being used in the fight against the Omega Metroid.
- God Never Said That: When Metroid: Samus Returns was released, some fans cited a wasted opportunity to make a Call-Forward by showing bosses from Fusion, such as Serris and Yakuza, in their natural habitat. However, the creatures canonically native to SR388 are only found in Sector 1; most bossesnote are of unknown origin. This confusion seems to stem from the fan-made Another Metroid 2 Remake, which includes Serris as a boss and provides lore referring to it as the apex aquatic predator of SR388.
- Jossed: To reconcile the differences between the Omega Metroids in Metroid II: Return of Samus and Fusion, it became a popular fan theory that the Omega Metroid in Fusion was genetically altered by the Galactic Federation to be larger, but artificially speeding up its metamorphosis came with the side effect of losing natural traits such as flight and Ice Beam immunity. This theory was ultimately disproven by Metroid: Samus Returns, which retconned the original Return of Samus by showing that Omega Metroids are naturally large, flightless, and vulnerable to the Ice Beam.
- What Could Have Been: The 2001 E3 preview, at that point simply titled Metroid IV, looked quite different and had several gameplay mechanics that didn't make it into the finished game, including it apparently taking place on a moving space ship rather than a station, and Samus having the ability to walk on walls (possibly inspired by the Spider Ball from Metroid II: Return of Samus). The trailer drew a great deal of criticism for looking like it belonged more on the Game Boy Color than the Game Boy Advance. With that feedback, Nintendo went back to the drawing board, and at the next year's E3 ran a preview looking much more like the finished game.
- Word of Dante: In official media, the only Fusion enemy with "-X" attached to the end of its name is the SA-X. Yet, it seems almost universally accepted among the fandom (including major Metroid fan websites such as Metroid Database, Metroid Recon, Wikitroid, and Metroid Wiki) that creatures infected and/or mimicked by the X parasites follow that naming scheme (Hornoad-X, Geemer-X, etc.). It's not clear if this originates from an obscure official source or if it is simply fanon that has become so well known that it's nearly indistinguishable from canon.
Trivia / Metroid Fusion