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"The dominant species of planet SR388, Metroids are energy-based parasitic predators. A Metroid will latch onto its prey and drain energy, growing larger as it does. The only way to shake an attached Metroid is to enter Morph Ball mode and lay a Bomb."
Metroid Prime's Logbook

The series' eponymous bio-form, engineered by the Chozo for the sole purpose of combating the most dangerous parasitic organism in the universe, the X. As an energy leeching predator, they either hatch from eggs laid by a Queen Metroid and evolve through a complicated metamorphosis into beasts capable of untold destruction, or divide by mitosis upon exposure to Beta rays. Their durability, aggression, and Explosive Breeder tendencies make them appealing bio-weapons to a number of unsavory characters throughout the galaxy; it's suggested that a benign use may be to use them to revolutionize energy usage and consumption.

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    General Tropes 
  • Achilles' Heel: They're really weak to ice attacks.
  • Adaptive Ability: At the cost of it being unable to reach its natural metamorphosis, Metroid Larvae can adapt to any environment they are in. This is how the Space Pirates were able to cultivate them on Tallon IV, and Phazon-mutated Metroids later make an appearance in Corruption. Samus Returns implies that the SR388 metamorphosis itself is an adaptation triggered by the planet's Aeion energy.
  • Antagonist Title: Played with. While a major enemy in every game they appear in and a primary driving force of the series, outside of Metroid II they aren't much more than mindless animals being used by the Space Pirates or Galactic Federation, making it more akin to a MacGuffin Title, and even a Secondary Character Title in Super Metroid (and Fusion, sort of) where the Hatchling is concerned. Subverted in Dread, when it's revealed that due to the injection of Metroid DNA she received in Fusion to save her life, Samus was gradually becoming a Metroid herself. At the end of the game, she fully awakens her abilities as a Metroid.
  • Arch-Enemy: Beyond being created to combat the X Parasite, Metroids were genetically programmed to see the Mawkin Tribe of Chozo as enemies. This grudge extends to even genetic samples from them, as Samus encountering Raven Beak awakened the Metroid DNA's killer instinct within her, beginning her slow metamorphosis into one.
  • Attack Animal: For the Chozo. The space pirates and Ing, not so much.
  • Big Eyes, Little Eyes: While the early instars don't have huge eyes, they're still somewhat proportionally large compared to how tiny they look on the later instars.
  • Bizarre Alien Biology: They are flying jellyfish with mouths like leeches and weakness to cold and/or missiles.
  • Bizarre Alien Reproduction: They usually have two known methods of reproduction, with their "normal" one being eggs laid by the Queen, who seemingly doesn't need any help to fertilize her eggs, and an alternative method being fission after exposure to Beta rays. This isn't even getting into how the Phazon mutated variants are able to propagate.
  • Breath Weapon: All stages of the SR388 Metroid metamorphosis post-larval can spit globs of corrosive ooze, bolts of electricity, and jets of flame as of Samus Returns.
  • Boss in Mook's Clothing: First two games, of the wolf pack variety. The second game even give them a funky battle theme.
  • The Cameo: Six Metroids make an appearance in Kirby's Dream Land 3, in the second stage of the Iceberg level, where they are required to be exterminated in exchange for the Heart Star. Much like in their native games, they can be defeated only by Kirby's Ice ability. For some reason, they are also incapable of harming Kirby, even when they successfully latch on him.
  • Clipped-Wing Angel: The effect of any Metroid adaptation in another environment, but particularly in the case of the unintended evolutionary cycle caused by imbibing Aeion from SR 388. As the Metroid develops into later stages of this cycle, they develop bodies of unbelievable and nigh-on unrivaled power, the usual Omega endpoint being plenty capable of butchering even Samus with ease with its crushing strength and talons. However, in mutating beyond the form the Chozo engineered, they lose something critical: the Nigh-Invulnerable nature possessed of natural "larval" Metroids, becoming susceptible to heavy artillery as that thick, gelatinous mass is dispersed amidst an armored carapace, leaving the nucleus vulnerable.
  • Combat Tentacles: Early artwork of Metroids depicts them with tentacles instead of fangs, which would suggest that they were originally intended to ensnare their victims with their tentacles while draining their energy. While this was dropped in later games, the idea was reused in Metroid Prime Trilogy, where the Metroid Prime, Hunter Metroids, and Metroid Hatchers prominently feature tentacles which they use in combat.
  • Cruel and Unusual Death: Getting your life-energy drained by a Metroid is not a very pleasant way to go. It's not clear what this life-energy is (according to the Pirates, it's not blood or any other body fluids), but whatever it is, not only will the victim die slowly and painfully as they have this energy sucked from them, they get reduced to a brittle, statue-like husk that will collapse into dust if so much as tapped.
  • Depending on the Artist: The Metroids' evolutions have different designs depending on the game. For example, in Return Of Samus and Fusion, the Alpha and Gamma Metroids lack visible mouths; the Zeta Metroid has a bulbous body and short, stubby limbs; and the Omega Metroid's head is more distinctly separated from its neck. Fusion also adds Giger-esque tube-like protrusions on the Omega Metroid's back. In Samus Returns and Dread, the Alpha and Gamma Metroids have unarmored mouths; the Zeta Metroid is much leaner and sleeker, making its xenomorph traits more pronounced; and the Omega Metroid's head is an extension of the main body while its own xenomorph traits are downplayed.
  • The Dreaded: In Federation Force, it's obvious the rank and file of the Federation are absolutely terrified of them.
  • Early Installment Character-Design Difference: Artwork for the first game depict Metroids with tentacles instead of fangs and four "cores" instead of the usual three.
  • Endangered Species: After Metroid II/Samus Returns, which is after Zero Mission and the Prime Trilogy. Samus personally drove them to this state.
  • Evolution Powerup: Instantly adapt to whatever planet they're brought to. The ones on SR388 are different from the ones from Zebes are different from the ones on Tallon IV are different from the ones on Aether... And that's not counting the ones on Bottle and Biologic Space Lab (GMOs) or the ones on Dark Aether (symbiotes with Ing).
  • Expy: Their infant jellyfish form and life-sucking abilities are based on the "Mermaid" jellyfish monster seen in the very end of the Rugball saga of Space Adventure Cobra. Their evolutions bring to mind the Xenomorphs from the Alien films.
  • Face Hugger: Metroid larvae, as well as similar strains such as Tallon Metroids and Phazon Metroids, attack by latching themselves onto the victim's head.
  • Flight: Unless explicitly told otherwise, never assume any of them are ground-bound, even if they look like it or have spent a large amount of time not in the air.
  • Foreshadowing: The first Metroid discovered by the galactic federation is a Human Popsicle. Hmm... and while they correctly theorize it to be a dangerous energy leeching creature that will multiply if exposed to beta rays for 24 hours, they're wrong about it being the reason for the downfall of civilization on SR388. No, they are the reason for that outpost...
  • Gone Horribly Wrong: They were created by the Chozo to act as a predator to the X Parasites on SR388. This worked out pretty well, but then the Metroids ran out of X to eat, so they moved on and began to feed on any other lifeform they could. This would have been mitigated by the Thoha propensity to reign them in, except the Chozo on the planet discovered something unforeseen: the very energy source of the planet that proved crucial in the Metroids' development caused them to begin mutating into further forms beyond the intended, becoming savage, unstoppable monsters who no longer heeded their makers. The Chozo thus attempted to destroy the planet to stop both the Metroids and the X but failed because the warrior Mawkin tribe saw the Metroids as perfect bioweapons and slaughtered the Chozo on SR388 to keep the planet intact. Fortunately, it is implied that the Chozo fully anticipated this, and raised Samus with the expectation that she would combat the Metroids too.
  • Graphics-Induced Super-Deformed: Metroids were originally depicted with tentacles in official art but their sprites looked more like mandibles, which the series just decided to roll with from the second game onward.
  • Insectoid Aliens: Alpha, Gamma, and Hopping Metroids are aliens that resemble insects, compared to their jellyfish-like or reptilian brethren.
  • It Can Think: Loosely implied in the original Return of Samus when you encounter a destroyed Chozo statue and its Ice Beam power-up relocated. Seeing as the only major thing active on SR388 at the time that could've done this would've had to be the Metroids, it implied that the later forms might just be intelligent enough to try to keep such a weapon from affecting them. Samus Returns undoes this by just having it at a Chozo statue like any other power-up, though at the same time the Metroids seem to generally be more intelligent and self-preserving across the board.
  • Joker Immunity: They are almost as bad as the Daleks in terms of going extinct and coming back — though the Daleks don't have the on-screen justification of total idiots trying to clone them. Subverted in Metroid Dread where the species is confirmed to be extinct with no signs of Metroids, cloned or otherwise, anywhere in the game unless you want to count our main protagonist, Samus Aran, as the last and most powerful Metroid in the universe.
  • The Juggernaut: Unless you go after their Achilles' Heel(s), even the most powerful attacks do little more than give them temporary pause. Given that they tend to hunt in packs, things have the potential to get very hairy, very fast.
  • Kill It with Ice: Though at first it was just "freeze them before a shower of missiles" — and even then, in the first installment they thaw out faster than any other freezable thing in the game. Later games make them explicitly weak to cold (although in Metroid II: Return of Samus, only infants and larva take such damage).
  • Killed Off for Real: By Metroid Dread, almost every last trace of Metroid DNA has been wiped out, meaning the Metroids are truly extinct and thus the species doesn't physically return to face Samus again. Instead, Samus ends being the target for Raven Beak, who is after her Metroid DNA to create a new cloned army. In a sense, Samus is the last Metroid left, though as a humanoid with Metroid powers rather than the floating jellyfish.
  • Lamprey Mouth: As of their revamped design in Metroid: Samus Returns, Alpha, Gamma, Zeta and Omega Metroids all have radial mouths lined with huge fangs.
  • Life Drinker: They prefer to eat Life Energy, and it's never proven if they can die from old age. They can drain all types of energy, but they'll get sick if they only eat electricity, for example. The Ing used them for their ability to feed directly off Phazon and not die, but had to be careful since Metroids still preferred to eat them.
    Pirate Notes: Metroid dissection continues to produce more questions than answers. Our research teams have isolated the energy conduits that run from the invasive twin mandibles to the energy core in the creature's quadripartite nucleus, but the manner in which the Metroid actually extracts the life force from its prey remains an utter mystery. The victim does not lose blood or any other vital fluids, and yet the Metroid extracts energy; identifying this energy is our central problem. It takes no physical form, and yet without it, the victim dies.
  • Living Battery: Super Metroid reveals that Metroids' ability to feed on ambient energy and impossibly efficient metabolisms make them an ideal power source.
  • Mascot Mook: Being the namesake of the franchise, it makes sense that Metroids are some of the most iconic creatures in the series.
  • Maybe Magic, Maybe Mundane: The Metroids drain an unidentified energy from their prey, and what this energy is may have been lost with the Chozo forever.
  • Meaningful Name: The word "Metroid" is a Chozo term describing a fearsome warrior; they were genetically engineered to be the perfect predator.
  • Mega Manning: Metroid Prime and the Super Metroid both steal and assimilate weapons used by the Space Pirates.
  • Metamorphosis Monster: Their exact lifecycle depends heavily on their environment, with the conditions of their native SR388 producing the most dramatic transformations. SR388 goes Infant-Larva-Alpha-Gamma-Zeta-Omega with some becoming Queens. Tallon IV have even weaker than normal Infant stage before Larva, which becomes Hunter or Fission. In Corruption we see Miniroids (in lieu of the regular Infant) becoming Phazon, which becomes either Hopping or Hatcher and possibly Prime.
  • Miracle-Gro Monster: Instead of metamorphosing, the Super Metroid just kept getting bigger, actually surpassing a Queen in size, being able to swallow Samus completely without the morph ball. Metroid Prime was also small at one point in time. Then there are the rapid maturing infant Tallon Metroids, the Space Pirates' failed attempt at a more manageable Metroid.
  • Names to Run Away from Really Fast: Metroid is revealed to be Chozo for "Ultimate Warrior".
  • Nigh-Invulnerable: Metroids by all conventional means are unstoppable. Missiles, lasers, catastrophic meltdowns; no amount of raw force applied short of a detonation between hundred gigaton to teraton visible out of oribt is enough to kill them outright. They possess one vulnerability in the form of cryogenic temperatures, which will turn their gelatinous forms stiff and just brittle enough that pumping them full of military-grade ordinance will finish the job.
  • Not Always Evil: The hatchling is, to date, the only "good" Metroid the series has shown. It's unknown whether or not its attachment to Samus can ever be replicated, since at the time, it was the last known Metroid. In Other M, Samus makes an attempt to bond with another (cloned) baby Metroid, but it only saw her as food. Samus Returns flashbacks show the larvae friendly to Chozo, only turning aggressive after their first metamorphosis. Eventually, an actually true good Metroid is shown in Dread: Samus herself.
  • Our Monsters Are Weird: The people in the story itself cannot make much sense out of them.
  • Palette Swap: In the first game, red Metroids always seek out Samus, though lazily, while green Metroids are a little more likely lie in wait but charge much faster. Their absence in Zero Mission indicates Canon Discontinuity. Echoes has red variants of Tallon Metroids, however they behave no differently than green Tallon Metroids seen in Prime before it.
  • Personal Space Invader: They were worse in the first game where it took multiple bombs to dislodge them, which might result in you accidentally being blown back into their grip. It only takes one to get them off in Metroid II and Zero Mission.
  • Power Floats: They're generally regarded as nigh-unbeatable monsters that rip the very life from your body. They also float through the air like alien jellyfish.
  • Removed Achilles' Heel:
    • The Tallon IV strands eventually outgrow their weakness to cold temperatures, trading it for others. The Super Metroid was also ice beam proof and could only be killed by Mother Brain's eye beam. All SR388 Metroids outgrew their ice weakness as well, but this detail was ignored by Metroid Fusion and retconned away in Metroid: Samus Returns.
    • The Space Pirates' long-term goals for the Metroids are to tame them so they'll follow orders and only attack other races, then remove their weakness to sub-zero temperatures, giving their organization an unstoppable army. In Other M, Adam and Samus find to their horror that the Federation has been thinking along similar lines, only with the utterly-suicidal oversight of having not trained the Metroids first, essentially taking a dreaded wild animal and making it invincible to anything short of flagship destroying weaponry.
  • Rousseau Was Right: As the Hatchling proves, Metroids are capable of emotional attachment and bonding, particularly right after hatching. The hatchling never evolves beyond the larval stage (only growing larger), so we never see whether or not the bond sticks through other stages of maturity. The Chozo Memories in Samus Returns implies that it does not stick, as the Chozo had to take action against the Metroids after they metamorphosed.
  • Shock and Awe: Alpha Metroids (in Samus Returns) and Gamma Metroids use electricity for ranged attacks or boosted defense.
  • Starfish Aliens: There is not a single thing in their biology that makes any sense by our standards.
  • Summon Bigger Fish: The basis of their existence. The Chozo were scared of the X, so they made the ultimate predator.
  • Super Not-Drowning Skills: In Return of Samus, one fight with an Alpha Metroid is underwater, or at least some kind of nonhazardous SR388 liquid. A fight with an Omega can go below liquid too.
  • Super Spit: An annoying trait of the SR388 Metroids as they develop (at least in Return Of Samus). Zeta spit is as short range as you'd expect but Omega spit doesn't just go far, it causes shock waves on the ground that can still damage Samus even if it misses her. And the Queen is even worse (unless Samus has the space jump and screw attack, which can negate the queen's projectiles when used together)
  • Turned Against Their Masters: As seen in the Chozo memories of Samus Returns, the Chozo were able to live alongside them for a time. After they started to metamorphose, they turned on their creators, forcing the Chozo to seal them in the caves beneath SR388.
  • Ultimate Life Form: In creating a natural enemy for a plasmatic parasite that can assimilate any form of organic matter with no vulnerabilities to them, the Chozo accidentally created the peak of the universal food chain with no equal. There is no naturally-occurring force that can kill a Metroid. Hit it with anything you want, it won't die. It will drain the energy from anything in its path, from an escape craft, to a power grid, to the door power keeping them from whatever terrified soul is behind it. The only vulnerability left to a Metroid is that which every living being in existence is vulnerable to by virtue of being a living organism: absolute zero temperatures, which will petrify it and turn it just brittle enough for a missile barrage to kill it. Even then, that's a window of seconds.
  • Vampiric Draining: No puncture wounds though. Those teeth/claws are used for gripping their victim, not as the mechanism for the draining.
  • Wave-Motion Tuning Fork: In Metroid: Samus Returns, Alpha and Gamma Metroids charge energy bolts between their three tusks before firing them.
  • Xenomorph Xerox: Their iconic jellyfish-like larval forms are basically floating Face Huggers, their later metamorphosis stages introduced in Metroid II: Return of Samus get progressively more Xenomorph-like (with the redesigned Zeta Metroids in Metroid: Samus Returns being nearly identical to them), they have a hive queen, they were created by the Chozo as bioweapons, and they are often seen by enemy factions as a potential weapon they can use which always bites them in the ass.

Specific Metroids

    The Metroid Hatchling
The Last Metroid
Debut: Metroid II: Return of Samus
"I next fought the Metroids on their home-world of SR388. I completely eradicated them except for a larva, which after hatching, followed me like a confused child..."
Samus Aran
The last Metroid in the galaxy after Samus exterminated the species on SR388 in Metroid II: Return of Samus (and Samus Returns). Recently hatched from an egg, the baby Metroid sees Samus and imprints her to be its mother. Samus, realizing that it's innocent and poses no threat, decides to spare and adopt the hatchling instead. As a result, the Metroid hatchling becomes a target for the Space Pirates, setting off the events of Super Metroid and affecting Samus's life in more ways than she could imagine...
  • Adaptational Badass: In Samus Returns, a remake of Metroid II, the Metroid hatchling is more proactive in its aid for Samus, especially during the new Final Boss fight with Proteus Ridley. When Ridley is about finish off Samus, the baby Metroid swoops in and drains a good portion of the Space Dragon's life energy. It does it several times during the last phase of the fight until Ridley finally falls down defeated..
  • Androcles' Lion: A major plot element in the series is how the baby repeatedly saves Samus's life, directly or indirectly, after she spared it.
    • In Metroid II, Samus is tasked with exterminating the Metroid species, but stops at killing a newborn showing no hostility toward her. In the extended ending of Samus Returns, Samus saves the baby from Ridley, and the baby returns the favor shortly afterward when it saves Samus from Ridley.
    • In Super Metroid, the baby is kidnapped, and Samus goes to get it back. Samus is eventually reunited with the Metroid, who is now gigantic after being nursed by the Space Pirates. It starts to swallow her, but recognizes her as its surrogate mother, and lets her pass. At the final fight with Mother Brain, the baby sacrifices itself to heal Samus and give her the hyper beam. This episode is the major thematic introduction for Metroid: Other M.
    • Later in Metroid Fusion, in a posthumous example, after Samus is infected by the X parasite, a cell sample of the same baby Metroid is used as part of the cure that destroys the parasites inside her and saves her life
    • In Metroid Dread, the baby's DNA enables Samus to outright become a Metroid, once again saving Samus's life when Raven Beak gains the upper hand in their final duel.
  • Badass Adorable: In Samus Returns, even when it hasn't been mutated by Space Pirate experiments, the little guy is dangerous enough to cause Ridley trouble.
  • Big Damn Heroes: During the final boss fight of Super and Samus Returns, the baby swoops in to save Samus right as the final boss is about to finish her off.
  • The Cavalry: Arrives in the nick of time for Samus in Super and Samus Returns. And sort of continues to be posthumously in Fusion as a vaccine infusion.
  • Chekhov's Gunman: In Super Metroid you could get the brief impression Samus was going to drop it off and do something else but the whole game turns out to be about it, especially the end of it.
  • Clone Army: The Metroids onboard the Bottle Ship and Biologic Space Laboratories research station were cloned from trace remnants of it left on Samus' armor, with the Federation intending to find a way to weaponize them (at least in the former case).
  • Damsel in Distress: A very atypical example, but Super Metroid sees the baby Metroid abducted by Ridley and Samus setting out to rescue it. "Damsel" on account of the baby being revealed to be an infant Queen, though given how much Bizarre Alien Biology is already in place regarding Metroids, it's anyone's guess how closely the baby Metroid actually aligns with any earthly conception of femaleness.
  • Energy Donation: A key-point of the plot in Super Metroid and a Metroid ability that has only ever been demonstrated by the hatchling. After attacking Mother Brain and saving Samus, it latches itself onto Samus and proceeds to top-off all of Samus's Energy tanks, and when the monsterous brain revives itself, protects Samus from Mother Brain in the process.
  • Extremely Protective Child: Just as Samus is the Mama Bear to it, the hatchling is just as willing to protect its foster mother in return.
  • Foil: To Samus. A gentle and innocent newborn with a bright future ahead of her until an alien invader kills all of its kind except itself. Additionally, the title of "The Last Metroid" applies to both characters, as Samus essentially becomes a humanoid Metroid by the end of Dread, with the rest of the species still extinct. The main difference being that Ridley spurned Samus's attempts to befriend him and became her Arch-Enemy while The Baby was Happily Adopted by Samus and ends up saving her life.
  • Foreshadowing: A case of a remake setting up a plot point for what would've been the original's sequel; Metroids giving energy is unheard of until the Hatchling performs it in the endgame of Super, but Samus Returns has the fight with Proteus Ridley make it voluntarily give bursts of energy to Samus, establishing this trait in advance continuity-wise.
  • Heel Realization: Just as it's about to finish Samus off, it recognizes her as its "mother" and chirps apologetically.
  • Heroic Sacrifice: One of the most iconic examples of the medium. The Super Metroid lets go of Samus and takes the full impact of Mother Brain's energy blast after she recovers. Its remains land on Samus, giving her the power she needs to destroy Space Pirate leader once and for all.
  • I Let Gwen Stacy Die: One of Samus's goals in Super Metroid was to rescue the baby Metroid from the clutches of the Space Pirates. Not only did she fail, but she also got to witness it die protecting her from Mother Brain. Samus mourned the hatchling's sacrifice and went into a period of self-doubt and depression shortly before the events of Other M, explaining her behavior in that game.
  • Implacable Man: None of Samus's weapons can so much as slow down the Super Metroid, not Power Bombs, not the Ice Beam, not Beam combos. Mother Brain had weapons able to damage and eventually kill it though.
  • Insect Queen: Since Other M's Metroid Queen is cloned straight from the baby and only special infants have the genetic coding to become queens, it would appear that the hatchling was indeed an infant Queen.
  • In-Series Nickname: It has many names given to it, usually by Samus herself. Baby, Metroid Hatchling and Super Metroid are the most notable of the bunch.
  • Last of His Kind: For a time it was in captivity, and the galaxy was at peace. Neither lasted, though all future Metroids can be traced back to this little one.
  • Secondary Character Title: After becoming the Super Metroid in Super Metroid. Averts Antagonist Title by being firmly on Samus's side, barring a few seconds of identity confusion.
  • Small Role, Big Impact: Though it's the most famous specimen of the series, the baby Metroid appears in only three games (not counting remakes), with its only major role being in Super Metroid where it gets stolen by the Space Pirates and later sacrifices itself to save Samus from Mother Brain. Yet this Metroid is the pivotal turning point of the storyline, marking the extinction of the Metroid species, the destruction of the Space Pirates, and the rise of the X Parasites. In fact, its DNA would be the foundation of Samus becoming the most powerful Metroid in Dread.
  • What Measure Is a Non-Cute?: Subverted as far as Samus is concerned. It's just as ugly as the other Metroids save for its tiny fangs, but its playful nature allows players to appreciate it more than its brethren, who are more likely trying to chow down on your head.
  • Your Size May Vary: In Super Metroid, they were not kidding. It had grown gigantic, covers Samus completely as opposed to the way Metroids usually just latch onto her head and was half the size of Mother Brain. The Other M version is significantly smaller, half the size of Samus at best.

    Metroid Prime 
The ultimate Phazon-mutated Metroid, capable of integrating technology into itself. By assimilating Samus's Phazon Armor it metamorphosed into Dark Samus. See Metroid - Metroid Prime and Dark Samus for both Prime and Dark Samus.

    The Most Powerful Metroid (HEAVY SPOILERS) 

Samus Aran

After receiving an infusion of the Baby Metroid's DNA to save her from being consumed by an X Parasite at the start of Metroid Fusion, Samus Aran gains an increasing number of Metroid abilities. By the time of Metroid Dread, her abilities have grown to the point Raven Beak deems Samus Aran "the most powerful Metroid of all".

For tropes concerning Samus see Metroid - Samus Aran.

Natural SR388 Strains

    Alpha Metroid

The first instar of Metroids past the famous larval form.

  • Attack Its Weak Point: Averted in Return of Samus, where the Alpha Metroid's entire body is vulnerable to missiles. Played Straight in Samus Returns, where it is only vulnerable to attacks aimed at its mouth and the nucleus on its chest.
  • Four-Legged Insect: Despite their insectoid appearance, Alpha Metroids only have four legs.
  • Insectoid Aliens: The Alpha Metroid vaguely resembles a pill bug.
  • Kill It with Ice: Subverted in Return of Samus. The Ice Beam has no effect on them like it does with the larvae, though thankfully they can be damaged by missiles without having to freeze them. Played straight in Samus Returns, where their nucleus can be damaged by the Ice Beam in case you run out of missiles.
  • Lamprey Mouth: As of their revamped design in Metroid: Samus Returns, Alpha Metroids have radial mouths lined with huge fangs.
  • Playing with Fire: Metroid: Samus Returns lets some Alpha Metroids use fire to drop projectiles and bolster their own defenses. Though getting frozen somewhat inhibits this ability so they can only use one or two fire-based attacks while their weak-point is coated in ice.
  • Powerup Let Down: In Return of Samus, the Alpha stage is weaker than the larvae. Despite now being immune to the Ice Beam, Alpha Metroids are slower, cannot latch onto their prey, and can be normally killed by missiles without needing to be frozen first. This makes Alpha Metroids a lesser threat to Samus and a lesser challenge to players when compared to the highly dangerous larval Metroids. Fortunately, this trope is averted in Samus Returns, which removes the Ice Beam immunity but makes up for it by making the Alpha Metroids' shell impervious to any missile that is not aimed at its mouth or nucleus, and Alpha Metroids now display electric or fire-based abilities that make them considerably more dangerous.
  • Red Eyes, Take Warning: In Samus Returns, Alpha Metroids have red eyes.
  • Shock and Awe: Metroid: Samus Returns lets Alpha Metroids use electricity to drop projectiles and bolster their own defenses. Though getting frozen somewhat inhibits this ability so they can only use one or two electrical attacks while their weak-point is coated in ice.
  • Wave-Motion Tuning Fork: In Metroid: Samus Returns, Alpha Metroids charge energy bolts between their three tusks before firing them.

    Gamma Metroid

The second instar of the original Metroid breed.

  • Attack Its Weak Point: Its mouth and the nucleus on its chest. For this reason, the Gamma Metroids frequently use electric bolts to deflect missiles aimed at their weak points in Return of Samus.
  • Breath Weapon: Gamma Metroids can spit bolts of electricity or jets of flame.
  • Cowardly Boss: In Samus Returns, some will flee to another nearby room through some webbing in the walls after taking a certain amount of damage, forcing Samus to pursue them.
  • Extra Eyes: Gamma Metroids have several clustered eyes, three on each side.
  • Four-Legged Insect: Despite their arachnid appearance, Gamma Metroids only have four legs.
  • Insectoid Aliens: The Gamma Metroid resembles a large spider.
  • Kill It with Ice: Subverted in Return of Samus. The Ice Beam has no effect on them like it does with the larvae, though thankfully they can be damaged by missiles without having to freeze them. Played straight in Samus Returns, where their nucleus can be damaged by the Ice Beam in case you run out of missiles.
  • Lamprey Mouth: As of their revamped design in Metroid: Samus Returns, Gamma Metroids have radial mouths lined with huge fangs.
  • Playing with Fire: Metroid: Samus Returns lets some Gamma Metroids use fire to shoot projectiles and bolster their own defenses. Though getting frozen somewhat inhibits this ability so they can only use one or two fire-based attacks while their weak-point is coated in ice.
  • Red Eyes, Take Warning: In Samus Returns, Gamma Metroids have red eyes.
  • Shock and Awe: Gamma Metroids are able to electrocute their prey. While they only use it to block Samus's missiles in Return of Samus, Metroid: Samus Returns lets Gamma Metroids use electricity to fire projectiles and bolster their own defenses. Though getting frozen somewhat inhibits this ability so they can only use one or two electrical attacks while their weak-point is coated in ice.
  • Wave-Motion Tuning Fork: In Metroid: Samus Returns, Gamma Metroids charge energy bolts between their three tusks before firing them.

    Zeta Metroid

The third instar of Metroids.

  • Attack Its Weak Point:
    • In Return of Samus, its back and the nucleus on its chest.
    • In Samus Returns, its mouth and the nucleus on its chest. Additionally, its back can be grabbed with the Grapple Beam during certain attacks, which will leave the Zeta Metroid stunned and lying on its side with its nucleus exposed.
  • Breath Weapon: In Samus Returns, Zeta Metroids can breathe jets of flame.
  • *Drool* Hello: How the first Zeta is introduced in Samus Returns.
  • Extra Eyes: Zeta Metroids have several clustered eyes, four on each side in Return of Samus and Samus Returns, three in Fusion.
  • Flight: In Metroid II, though this ability seems to have been retconned as of Samus Returns.
  • Kill It with Ice: Subverted in Return of Samus. The Ice Beam has no effect on them like it does with the larvae, though thankfully they can be damaged by missiles without having to freeze them. Played straight in Samus Returns, where their nucleus can be damaged by the Ice Beam in case you run out of missiles.
  • Lamprey Mouth: Zeta Metroids have radial mouths lined with huge fangs.
  • Raptor Attack: In the Zeta phase, Metroids heavily resemble raptors.
  • Red Eyes, Take Warning: In Samus Returns, Zeta Metroids have red eyes.
  • Super Spit: Zeta Metroids can spit globs of corrosive ooze. In Return of Samus, their spit is as short range, but Samus Returns lets them spit across the room. In one attack, the Zeta Metroid spits multiple globs in different directions that continue to bounce off walls.
  • Xenomorph Xerox: The Metroids in general have many similarities to the Xenomorphs from the Alien franchise, but it's most apparent with the Zeta Metroids, especially in Samus Returns where they look and act almost identically to their famous adult forms.

    Omega Metroid

The penultimate instar of Metroids and the highest most are capable of achieving.

  • Attack Its Weak Point:
    • In Return of Samus, the nucleus on its chest can still be damaged but is much more durable compared to earlier stages. However, shooting an Omega Metroid in the back deals much more damage than usual. Using this method, only 14 missiles are needed to kill an Omega Metroid.
    • In Fusion, the nucleus on its chest is the Omega Metroid's only vulnerable area.
    • In Samus Returns, its mouth and the nucleus on its chest. Here, the nucleus is covered with a layer of armor that must be blown off before it can be damaged.
  • Bait-and-Switch: When you defeat the final Zeta Metroid, you'll find that the shifting acid has actually trapped you in the area rather than opened up the next area like usual. You have to circle back to the room the Zeta was in (or the adjacent room in Samus Returns) to find the first Omega Metroid waiting there.
  • Breath Weapon: It can spit fireballs in Metroid II and graduates to a full laser beam in Samus Returns.
  • Collapsing Ceiling Boss: In Samus Returns it can slap its tail on the ground, causing boulders to rain from the ceiling. In later stages it combines this with an attack that ignites the floor, dealing damage if Samus lands.
  • Damage-Sponge Boss: In Return of Samus, an Omega Metroid is not significantly tougher than a Zeta Metroid. However, the Omega Metroid makes up for it by being incredibly durable, requiring about forty missiles to be killed (unless the player exploits its weakness).
  • Early-Installment Weirdness: In Return of Samus, the Omega Metroid is only slightly taller than Samus, immune to the Ice Beam, able to fly, and depicted with a hairy mane in official artwork. In Fusion and Samus Returns, the Omega Metroid is giant, weak to the Ice Beam, unable to fly, and completely hairless.
  • Extra Eyes: It has several clustered eyes, four on each side in Fusion and Metroid II, five in Samus Returns.
  • Final Boss: A Metroid clone evolves into an Omega in Fusion, and is the final boss of the game. Depending which game you bought first, the Omega Metroid is either the second or third Metroid final boss, since Metroid Prime was released on the same day as Fusion, and the first eponymous Prime is chronologically the final boss of its game.
  • Flight: In Metroid II, though this ability seems to have been retconned as of Fusion and Samus Returns.
  • Goomba Stomp: One of its attacks in Samus Returns is to leap towards Samus, crushing her beneath it.
  • HP to One: The Omega Metroid in Fusion drops Samus to a single point of energy with just one hit. However, since this is a scripted event, she will always be reduced to one point, whether she was at full health or already at one.
  • Kill It with Ice: Subverted in Return of Samus. The Ice Beam has no effect on them like it does with the larvae, though thankfully they can be damaged by missiles without having to freeze them. Played straight in Fusion, where the Omega Metroid is only vulnerable to the Ice Beam, and Samus Returns, where their nucleus can be damaged by the Ice Beam in case you run out of missiles.
  • Lamprey Mouth: Omega Metroids have radial mouths lined with huge fangs. This is more pronounced in their revamped design in Metroid: Fusion and is reflected by their entire design, which now resembles a lamprey with limbs.
  • Lightning Bruiser: Don't let its size fool you, its capable of moving quickly when it needs to.
  • Post-Final Boss: One serves as this in Fusion, after escaping the Restricted Laboratory as a larva and quickly evolving by feeding on the numerous X.
  • Red Eyes, Take Warning: In Fusion and Samus Returns, Omega Metroids have red eyes.
  • Tail Slap: In Samus Returns, not only will they swing their tails around to hit Samus, they will also pound the ground with their tails to drop rocks from the ceiling on her.
  • T. Rexpy: Much like how the Zeta resembles a raptor, the Omega resembles an alien Tyrannosaurus rex.

    Queen Metroid

The ultimate form a Metroid can achieve, although only a few have the genetic predisposition to do so. A Queen is a major threat to any ecosystem due to its ability to continuously breed more Metroids.

  • Acid Attack: Can spit out globs of acid at Samus in Return of Samus and Samus Returns.
  • Big Bad: The Queen in Return of Samus and Samus Returns, as the creator of the Metroids Samus hunts throughout the game and the apex predator of SR388.
  • Breath Weapon: In Other M, after destroying its Metroid offspring, it grows crystalline spikes on its neck and gains the ability to breathe fire. This ability was later retconned into Samus Returns. The latter game also gives the Queen the ability to breathe a powerful gust of wind to blow Samus back, usually after igniting the wall with fire or spitting out floating globs of acid.
  • Contrasting Sequel Antagonist: Compared to Mother Brain, who is an intelligent supercomputer whose goal is to conquer the galaxy, the Queen Metroid is simply a feral creature that is protective of its offspring.
  • Depending on the Artist: The Queen Metroid's design differs upon each game. In the original Metroid II, the Queen Metroid's head is closer to its body like a turtle, extending its neck periodically to attack Samus. In Other M, the Queen's neck is always long, never extending or retracting like in its debut appearance. This is retained in Samus Returns, which adds new additions to the design such as a long tail and a larger cluster of eyes that glow red.
  • Early-Installment Weirdness: In Return of Samus, the Queen Metroid can extend her neck, and she spits out unidentified projectiles that can be rendered harmless with the Screw Attack. In Other M and Samus Returns, the Queen Metroid's neck is a fixed length, and she breathes fire that is dangerous even while using the Screw Attack. She is also vulnerable to standard Morph Bombs in Return of Samus, but that is because the Power Bomb was not yet introduced in the series.
  • Extra Eyes: It usually has four eyes per cluster. Samus Returns increases the cluster number to six.
  • Feed It a Bomb: Its major weakness. Samus can enter its mouth via Morph Ball and drop a few bombs into its stomach, causing massive damage in its internal organs. Power Bombs are exceptionally useful in these situation.
  • Final Boss: The Queen Metroid serves this role in Return of Samus and Other M, the fight with MB being more a Post-Final Boss. In Samus Returns, she loses the title and becomes the penultimate boss thanks to Ridley showing up at the very last second.
  • Flunky Boss: In Other M, the Queen Metroid can release Metroids stored in its back to attack Samus. However, it has a limited number and once those six Metroids go down, the Queen has to fight Samus directly.
  • God Save Us from the Queen!: Especially when the Queen is a gigantic dinosaur-like alien monster.
  • Homing Projectile: The Queen Metroid shoots what is a mix between this, Spread Shot and Pinball Projectile in Return Of Samus.
  • Inexplicably Tailless: Inverted. The Queen Metroid in Samus Returns has a long reptilian tail that its previous appearances did not have.
  • Insect Queen: Given its title and being the source of the Metroids, this is no surprise.
  • King Mook: To the Metroids.
  • Large and in Charge: The Queen is much bigger than any of the other Metroid instars.
  • Mama Bear: Harming Metroids (which are its children) will enrage the Queen.
    • In Metroid II and Samus Returns, the Queen Metroid is protecting the last Metroid egg from Samus to the bitter end. When all the Metroids in its labyrinth are killed, the Queen Metroid can be heard roaring in rage.
    • In Other M, when the Metroids are frozen by Samus's Ice Beam and fall to the ground, the Queen Metroid will stomp on the floor to break them free from the ice. When all the Metroids are dealt with, the Queen goes completely berserk, forming a near-impenetrable crystalized armor around its neck and attacking Samus directly.
  • Monster Lord: Again, to the Metroids.
  • Monster Progenitor: The Queen Metroid lays the eggs that hatch into Metroids. As such, nearly all the Metroids can be traced back to the Queen.
  • More Teeth than the Osmond Family: It has a mouth full of sharp teeth like a crocodile, with additional sets on the sides of its jaws.
  • Non-Malicious Monster: Considering that you are hunting down and killing its children, it has every right to be angry and aggressive towards you.
  • Pre-Final Boss: In Samus Returns, while still the Big Bad and a challenging, climactic opponent at the end of the game, is not the Final Boss like in the original. Instead, Ridley shows up at the landing site and becomes the new Final Boss.
  • Red Eyes, Take Warning: The remake Samus Returns turns Queen Metroid's eye clusters from blue to red.
  • Stationary Boss: If you can't beat it, you can leave and come back with more ammo. Samus Returns averts this by having the Queen move around a little.

Artificial and Phazon-mutated Variants


Extremely weak Metroid clones found in Maridia. They are the result of the Pirates' early attempt to engineer Metroid specimens.

  • Bait-and-Switch: Likely the first time the player will see a Mochtroid is when rapidly travelling through the vertical tube connecting upper and lower Maridia. In that blurry split second, you might assume that the standard Metroids have somehow escaped Tourian. It's not until you circle around to the middle section of Maridia on your way to fight Draygon that you find out the Mochtroids actually look different from regular Metroids and are much weaker.
  • Clone Degeneration: Sure, they drain Samus's energy, but they can't latch onto her properly, and they are weak against any weapon, not just ice and missiles. And they don't even have the right number of nuclei.

    Tallon Metroid
A strain of Metroids cultivated from the few specimens the Space Pirates salvaged from their base on Zebes and modified by experiments with Phazon on Tallon IV. Despite having the same general shape as the natural larval form, they are distinguished by being weak against all weapons besides the Ice Beam and Missile combo and, when later encountered on Aether, a red outer membrane rather than the green one more commonly associated with Metroids.
  • Dub Name Change: In English, this strain was simply called "Metroid" in Metroid Prime, but in Spanish, it was called "Metroid Talloniano" even before Echoes gave Tallon Metroids a specific designation.
  • Gone Horribly Wrong: The infant Tallon Metroid, a state that exits the egg less developed than even a larval Metroid. The Space Pirates created this state to be more manageable Metroids, with the idea they would serve as portable batteries; unfortunately, Infant Tallon Metroids are mindlessly aggressive, flinging themselves with reckless abandon at all living things, and can mature beyond the larval stage within seconds if they make contact with a large enough concentration of phazon (a puddle is enough).
  • Miracle-Gro Monster: The rapid maturing infant Tallon Metroids, which are the Space Pirates' failed attempt at a more manageable Metroid.
  • Named in the Sequel: This strain was originally called "Metroid" in Metroid Prime (barring the Spanish Dub Name Change), but was given the more specific moniker "Tallon Metroid" in Metroid Prime 2: Echoes. The name retroactively made its way back into the Nintendo Switch remastered version of Metroid Prime.
  • Overnight Age-Up: Infant Tallon Metroids on Aether will instantly grow into adults when exposed to Phazon.
  • Palette Swap: Echoes has red variants of Tallon Metroids. However, they behave no differently than green Tallon Metroids seen in Prime before it.

    Hunter Metroid

A heavily mutated and misshapen evolution of the Tallon Metroid.

  • Body Horror: Standard Metroids already look pretty freaky, but Hunter Metroids nonetheless manage the impressive feat of looking like horribly deformed Metroids.
  • Combat Tentacles: One of its fangs has been turned into a tentacle that it uses to snag prey from a distance.
  • Power Up Let Down: Being able to drain energy from range was probably a useful adaptation against normal wildlife, but against advanced lifeforms it just removes the Interface Screw of locking onto their head and obscuring their vision. As a result, it's much easier to kill them as they float in place a few feet away.
  • Red and Black and Evil All Over: Their membrane is red, while their hooked fangs and tentacles are black.

    Fission Metroid

A variant of the Tallon Metroid found mainly in the Impact Crater. Upon taking a certain amount of damage, it will split into two Fission Metroids that are only weak against one particular beam weapon.

  • Asteroids Monster: A Fission Metroid will split into two Metroids when sufficiently damaged, each of which is only vulnerable to a specific beam weapon.
  • Color-Coded for Your Convenience: Much like the Pirate Beam Troopers, Yellow Fission Metroids are only weak against the Power Beam, Purple ones against the Wave Beam, White ones against the Ice Beam, and Red ones against the Plasma Beam.
  • Ledge Bats: Fission Metroids in the Impact Crater in Prime. They obscure your visor when they latch on, making jumps even harder, the morph ball tends to roll off slopes and they can lift the morph ball as well as the bouncing bomb explosions to detach them cause potentially sending you off the edge.
  • Mutants: Explicitly referred to as such in their scans, as the Phazon exposure has screwed them up so much that it's given them the ability to split into two unstable copies, each with a different but still-random Beam weapon weakness.
  • Respawning Enemies: The Fission Metroids in the Phazon Core of the Impact Crater will never stop spawning out of the red Phazon even if you kill all the ones present in one go. Even worse, they will not stop chasing Samus down as long as she's in the room.
  • Unique Enemy: In the original North American release of Prime, Fission Metroids only appeared in the Impact Crater. The European and Japanese releases, Prime Trilogy, and Remastered added them to a few rooms in the Phazon Mines after defeating the Omega Pirate.

    Dark Tallon Metroid

A Tallon Metroid that has been possessed by an Ing.

  • The Cameo: One shows up in Corruption as a dissection subject.
  • Demonic Possession: As one might guess from the "Dark" moniker, they're metroids that have been possessed by Ing.
  • Eyes Do Not Belong There: Regular Tallon Metroids don't have any eyes, but Dark Tallon Metroids gain an off-center yellow eye upon Ing possession.
  • Make My Monster Grow: They increase in size by absorbing Phazon energy.
  • Wild Goose Chase: The subject of a scientific version. The pirates in Corruption are apparently trying to research what caused them to become more durable and intelligent upon introduction to Dark Aether's atmosphere. Since they're working under the assumption that it was something in the atmosphere that caused the "mutation" and lack the relevant knowledge about the Ing to know they were possessed, their research is doomed to failure.

    Phazon Metroid

A heavily mutated Metroid strain. It is most notable for the ability to phase through solid matter. The Space Pirates made heavy use of these creatures during their all-out assault on the Galactic Federation during the Phazon crisis.

  • Attack Its Weak Point: Using the Nova Beam along with the X-Ray Visor lets you directly attack its nucleus for a quick kill.
  • Batman Can Breathe in Space: Phazon Metroids, which to be fair, may be because of their ability to leave local spacetime, but Miniroids do it too without that benefit.
  • Intangible Man: Phazon Metroids hatched by the Metroid Hatcher that can only be killed with Hypermode (or just waiting them to come back to local space time).
  • One-Hit Kill: Using the X-Ray visor with the Nova Beam allows you to bypass their tough outer shell and target their nuclei directly, which kills them in one shot.

    Hopping Metroid

A completely ground-based Phazon mutation of the Metroid.

  • Ground Pound: How Hopping Metroids attack after entering hyper mode.
  • Powerup Let Down: Despite being mutated from Metroids, the Hopping Metroid can't even fly.
  • Related in the Adaptation: In the English version of the game, the Hopping Metroid and Phazon Hoppers are incredibly similar but unrelated species, with Phazon Hoppers presumably being Phazon-corrupted versions of the Hoppers naturally found on Bryyo. The Japanese version's Logbook states that Phazon Hoppers are actually an even more mutated stage of Phazon Metroids, with Hopping Metroids being the Phazon Hopper's immature stage.
  • Suspiciously Similar Substitute: The lore states that Metroids will only reach the Gamma stage when living on SR388 or a close facsimile. But, the Phazon-mutated strains still have the later form of Hopping Metroids that heavily resemble the Gamma Metroid.
  • Underground Monkey: It has the same animations and behavior as the Phazon Hoppers. In the Japanese version of the game, the similarities are explained by Phazon Hoppers being mature Hopping Metroids.

    Metroid Hatcher

An advanced strain of Phazon Metroid that is capable of spawning more Metroids.

  • An Arm and a Leg: Defeating a Metroid Hatcher involves ripping off its tentacles with the Grapple Lasso.
  • Attack Its Weak Point: The tips of the tentacles must be shot until they withdraw into its body, after which its mouth becomes the weakpoint. Once the mouth is shot and the hatcher is stunned the protruding tips of the tentacles become weak points again, this time for the grapple lasso rather than your traditional weapons.
  • Boom, Headshot!: Nova Beam (which phases through their armor to hit their nuclei) + X-Ray Visor (which allows you to see aforesaid nuclei) = dead Hatcher.
  • Cognizant Limbs: Its main body is protected by phazite platting, the tentacles that it attacks you with are not. It's like the game is trying to tell you something. When using seeker misses the tentacles can be targeted individually and independent of the rest of the hatcher.
  • Combat Tentacles: Similar to Hunter Metroids, Metroid Hatchers have long tentacles that use in combat.
  • Degraded Boss: Two Metroid hatchers appear after the first, but by then Samus has obtained upgrades that allow her to bypass their armor and kill with a single shot.
  • Heal Thyself: They can recover health by sticking their tentacles in Phazon pools.
  • Mini-Boss: Metroid Hatchers are about on par with the other minibosses in Corruption, despite their non-unique nature.
  • Mook Maker: Can spawn Phazon Metroids.
  • Skippable Boss: Encountering at least one Metroid Hatcher is required to beat the game. Fighting both is only necessary for 100% completion. Beating them makes the game easier even if you aren't interested in getting everything, since one is guarding a shortcut and another an energy tank. In one case, the doors do not even lock after the Hatcher emerges, allowing the player to simply run past it after the cutscene concludes; it will be waiting by the door every time you enter the room but can be avoided indefinitely.