Cowboy BeBop at His Computer: The game was briefly shown on an episode of House, with the titular doctor making an offhanded comment about being on "Level Four." Problem is, Metroid doesn't use numbered levels.
Fan Nickname: The Final Boss droid shaped like Ridley has been dubbed "Mecha-Ridley" by fans, in comparison to Ridley's cyborg form "Meta Ridley". However, other sources and circles may call it the "Ridley Robot" instead.
For reasons unknown, the speedrunning community calls it Iron Ted.
What Could Have Been: Artistically, Zero Mission was originally designed with a cartoony look that resembled a more detailed version of the original game's graphics. The design team later changed it to the mostly realistic-looking version it is now, after deciding a game with more realistic graphics would do better in North America, where the franchise is more popular.
Crocomire can be found in the game's files, seemingly indicating that he was going to be included in the game (and the game was meant to tie into Super Metroid more), but was ultimately cut. Interestingly enough, the Crocomire sprite here lacked the rough skin traditionally found on Crocomire, indicating that the player would damage Crocomire due to in-game events.