History UniqueEnemy / Metroid

** A Mini-Kraid is encountered only once through the whole game, in the room right before the actual Kraid. It may be a nod to the boss's originally being much smaller in the first and this enemy might be here to showcase the evolution of the character.

** Maridia has the most unique creatures out of any area, possibly a TruthInTelevision reference to the wide variety of life found in the oceans.

** The Dachora and Etecoons that taught you moves to get out of certain traps earlier in the game can be saved at the end by entering a side room and shooting the wall during the escape sequence. No reason [[VideoGameCaringPotential other than to help those who helped you]]. They actually appear again in [[spoiler:the final escape sequence in ''VideoGame/MetroidFusion''. ''Where they steer your ship away from the final boss to avoid destruction and bring it back to you at the end, effectively saving you'']].

** [[http://metroid.wikia.com/wiki/Ice_Shriekbat Ice Shriekbats]] only appear in one room in the entire game (the Ice Ruins West area of Phendrana Drifts) and are ''infamous'' for how easy it is to [[PermanentlyMissableContent lose]] their MonsterCompendium entry if you don't watch for them. They blend in with the rocks they roost on until you get close and can be easy to mistake for the [[ComMons very common]] ordinary [[GoddamnedBats Shriekbats]] you've probably already scanned. When you get close they dive bomb into you killing ''themselves'' in the process and [[PunctuatedForEmphasis They! Don't! Respawn! EVER!!]] Even if they don't kill themselves, miss them and they disappear as soon as you get the nearby suit upgrade never to appear again, making it impossible to fill your logbook [[HundredPercentCompletion completely]]. Thankfully, the PAL version fixes this so they do {{respawn|ingEnemies}} and no longer arbitrarily disappear from the game if you miss them.

** The hallway just before Ridley has two silver "ninja" Space Pirates. The only other place they appear is during the escape sequence, where they are instantly eviscerated by Samus' Hyper Beam.

* ''VideoGame/MetroidIIReturnOfSamus'': Unlike ''[[VideoGame/MetroidSamusReturns the official remake]]'', this game includes some very rare enemies that only appear once or twice:

** The Dachora and Etecoons that taught you moves to get out of certain traps earlier in the game can be saved at the end by entering a side room and shooting the wall during the escape sequence. No reason [[VideogameCaringPotential other than to help those who helped you]]. They actually appear again in [[spoiler:the final escape sequence in ''VideoGame/MetroidFusion''. ''Where they steer your ship away from the final boss to avoid destruction and bring it back to you at the end, effectively saving you'']].

*** A red Skultera only appears in a single room that connects to Brinstar. Asides from it's color, it's identical to the other Skulteras found throughout the game.

** There's a bonus enemy called the "Armored Pirate" that only appears in [=Elysia=] in the NTSC version of the game (meaning it isn't in the ''Trilogy''). It appears to have been added by mistake, being physically identical to the Armored Pirate Militia and not appearing in the Logbook once you scan it. But because of its existence, it's possible to get an unnatural 109 Red Credits.

** This game has a few in Maridia, mostly for functional reasons: In one corridor, a bizarre walker by the name of Shaktool carves a path through a wall for the player that eventually leads to the Spring Ball add-on. Later in the same segment, a corridor contains a squirming pile of white...things to help show off one of the abilities of Samus' new found equipment.
** Maridia also has a large turtle-like creature accompanied by little baby turtles. Its purpose is to help reach a missile pack that would otherwise require Space Jump (which you only get later) to reach.

** The hallway just before Ridley has two silver "ninja" Space Pirates. The only other place they appear is during the escape sequence.

*** The other is the Webling, which are similar but don't block doors. They are only found in the Feeding Pit Access in the Dark Agon Wastes, and can be killed with the Light Beam.

** There are two kinds of Ing barriers that hardly appear at all.

*** The other is the Webling, which are similar but don't block doors. They are only found in the Feeding Pit Access in the Dark Agon Wastes, and can be killed with the Light Beam. Like the Ing Webtrap, they count towards 100% Logbook, so if you're going for it, don't forget to scan these guys first.

*** The other is the Webling, which are similar but don't block doors. They are only found in the Feeding Pit Access in the Dark Agon Wastes, and can be killed with the Light Beam.

** Since your time spent on Phaaze is limited, there are many lifeforms that you can breeze past if you're in too much of a hurry. These include the Maw, the [=EyeballBlocker=], the Aazelion, and more.

** Since your time spent on Phaaze is limited, there are many lifeforms that you can breeze past if you're in too much of a hurry. These include the Maw, the EyeballBlocker, the Aazelion, and more.

** There's a bonus enemy called the "Armored Pirate" that only appears in [=Elysia=] in the NTSC version of the game (meaning it isn't in the ''Trilogy''). It appears to have been added by mistake, being physically identical to the Armored Pirate Militia and not appearing in the Logbook once you scan it. But because of its existence, it's possible to get an unnatural 109 Red Credits.
* ''VideoGame/MetroidIIReturnOfSamus'': Unlike ''[[VideoGame/MetroidSamusReturns the official remake]]'', this game includes some very rare enemies that only appear once or twice:
** Only two Blob Throwers are in the game, both located on the roof of the Chozo ruins in Phase 3.
** Only a single Shirk is found in the entire game, located in Phase 4.
** Two Automs, which are the only ones in the game, share the same room as the Shirk.
** Only two Ramulkens are in the game, with one found in Phase 7 and the other found in Phase 8.
** Only two Gunzoos are in the game, both located in the Chozo ruins in Phase 7.
** There are some other enemies that are more common than the aforementioned enemies but are each found in only a single room. These include Senjoo, TPO, Meboid, Proboscum, Gravitt, Skreek, and Drivel.

** The hallway just before Ridley has two "ninja" Space Pirates. The only other place they appear is during the escape sequence.

** There's a bonus enemy called the Armored Pirate that only appears in [=Elysia=] in the NTSC version of the game (meaning it isn't in the ''Trilogy''). It appears to have been added by mistake, being physically identical to the Armored Pirate Militia and not appearing in the Logbook once you scan it. But because of its existence, it's possible to get an unnatural 109 Red Credits.

** There's a bonus enemy called the Armored Pirate that only appears in the Concourse in [=Elysia=] in the NTSC version of the game (meaning it wasn't in the ''Trilogy'' version). It appears to have been added by mistake, being physically identical to the Armored Pirate Militia and not appearing in the Logbook once you scan it. Because of its existence, it's possible to get an unnatural 109 Red Credits.

** Interestingly, there's a bonus enemy called the Armored Pirate that only appears in SkyTown in the NTSC version of the game (meaning it wasn't in the ''Trilogy'' version). It appears to have been added by mistake, being physically identical to the Armored Pirate Militia and not appearing in the Logbook once you scan it. Because of its existence, it's possible to get an unnatural 109 Red Credits.

* ''VideoGame/MetroidPrime3Corruption'' has a few examples including the fast and [[ThatOneSidequest incredibly hard to scan]] Gel Ray found in pools of Fuel Gel.

** This game has a few in Maridia, mostly for functional reasons: In one corridor, a bizarre walker carves a path through a wall for the player. Later in the same segment, a corridor contains a squirming pile of white...things to help show off one of the abilities of Samus' new found equipment.

** There's also Ice Parasites that only appear in two rooms and disappear from the game, there are several other one-time scans in this series too, but luckily they're not quite as easy to miss as the Ice Shriekbats (for one, they don't fly at you and explode on your face as soon as you get close). Same with the Aqua Drones, which appear in one room and disappear after that.
** Ram War Wasps are only spawned by the Hive Mecha miniboss. Once it is defeated, they are never seen again. Ditto the Barbed War Wasps in the Incinerator Drone chamber.

* ''VideoGame/MetroidPrime2Echoes'' has the Lightbringers, which are living, walking safe zones that crawl on walls. Interesting game mechanic that could have been used in a lot of places... but no, you only got to see three of them in a room near the beginning of the game, and they're gone when you come back later.

* ''VideoGame/MetroidPrime3Corruption'' has a few examples including the fast and [[ThatOneSidequest incredibly hard to scan]] Gel Ray found in pools of Fuel Gel.

** There is a [[http://metroid.wikia.com/wiki/Geemer unique Geemer]] colored like Samus's Varia Suit which mimics her movements above a particular room in Crateria. If you leave the room, it will be gone when you reach its spot. It doesn't do anything or drop anything special, it can't hurt you, and there is no explanation for it.