The Big Metroid was an anomaly in the Metroid life cycle seen in Super Metroid and briefly in Other M. Normally, when a Metroid is not located in the environment of its homeworld, SR388, and is instead inserted on another planet, the different atmosphere and climate seemingly halts the Metroid's natural life cycle and the creature is never able to mutate into the Alpha stage.
However, a never-before-seen mutation occurred with Samus Aran's baby (the last surviving Metroid from SR388's extermination) when it was brought to the planet Zebes. Stolen by the Space Pirates from the Ceres Space Station during a raid led by Ridley, the Metroid was not only restricted to its larval stage, it had also, for reasons unknown, increased dramatically in size. Its leeching attack was far greater than that of a typical Metroid, and it had somehow removed its vulnerability to cold temperatures (an invulnerability seen previously in several Phazon-induced Metroid mutations, and Unfreezable Metroids later on). This mutation was never witnessed within other Metroid specimens on Zebes featured in Metroid, its remake Zero Mission and earlier Metroids encountered in Super Metroid.
This giant Metroid is practically immune to all of Samus' weaponry, including the Ice Beam and Power Bombs. Only Mother Brain had the strength to harm it and ultimately kill it; while the Pirate leader was capable of killing it with one of its standard attacks in Super, Other M 's interpretation revealed that she had to rely exclusively on her Laser Brain Attack to destroy it.
Interestingly, the Big Metroid was capable of performing an ability that no other Metroid had previously shown: the ability to transfer energy from one being to another. This life-saving power, originally hinted at by the Ceres scientists' research as possibly being beneficial to Galactic society in Super Metroid 's introduction sequence, allowed Samus to emerge victorious in her battle with Mother Brain.
The reason behind this mutation is never explained in-game. In the Super Metroid comic, Armstrong Houston suggests that the creature was heavily exposed to beta rays which resulted in its unnatural size increase; since the baby was the only existing Metroid during Super Metroid 's events, it is probable that the Space Pirates were forced to use an excessive amount of beta radiation to produce a satisfying amount of Metroids, thus mutating it. This would also explain why the Metroids featured in Samus's Zero Mission did not turn into Big Metroids despite exposure to beta rays. However, since it is stated in Other M that only special Metroids have the specific genetic coding to become Queen Metroids and the Queen featured in the same game was created from the baby's DNA, it is possible that the Big Metroid was a stage in the baby's evolution into a Queen.
The battle against the Big Metroid is scripted in the game. As mentioned before, it is invulnerable to all of Samus' weapons and it is programmed to chase her at an incredible speed and weigh her down as it drains energy off of her, preventing her from leaving the room where it is "fought". It cannot kill Samus, since it is also programmed to stop exactly when one unit of energy remains, triggering the cutscene where the Big Metroid recognizes Samus. However, it is nevertheless possible to "defeat" this creature: Samus can successfully evade the Big Metroid's persistent chase and leave the room using quick maneuvering of her jumping abilities without triggering the mentioned cutscene (a popular tactic among speedrunners). However, if the Metroid is latched onto Samus as she exits the room, she will be glitched in the form of incredible slowdown in her movements, exactly as if the creature was still weighing her down. Another glitch that can result from having the Big Metroid latch onto Samus before leaving its room is the heroine being frozen in her exhausted animation (hit by the Laser Brain Attack and her near-complete energy absorption), unable to recover. Therefore, these glitches force players to reset their consoles.
"There's nothing you can do to get it off of you."
- Matt Manchester, an environment artist for Metroid Prime 3: Corruption, wrote design notes explaining why the Metroid increases in size, but they are not considered canon as they did not make it into the final game due to text size limitations: "Observations of captive Metroids display a rare anomaly in their developmental growth. Approximately .08% of contained specimens never reach the biological process that leads to their otherwise natural metamorphic stages of maturity. While developmental stages are stunted, physical growth continues at a congruent rate. Efficiency of energy consumption increases steadily as well. During behavioral analysis, greater intelligence and problem solving skills are observed. Heightened abilities of energy consumption make this anomaly a potential key in isolating and duplicating their feeding process artificially." In his notes, he considered placing a Big Metroid in a containment in Metroid Processing, though this never came to fruition: "In one chamber, I wanted to put a fat giant metroid, like in the end of Super, and then tie in an explanation as to why some Metroids (like the one in Super) get really big in their larval state, but others evolve into more adult forms. Again, none of this is canon by any means, but just the fiction I wrote for myself when making the room."
- Interestingly enough, the Omega Metroid seen at the end of Metroid Fusion also suffered from an unnatural growth. Since this Metroid was also cloned from the baby like the Queen Metroid in Other M, it may also have been transforming into a Queen. However, this was never confirmed.
- The first encounter with the Big Metroid is accompanied by the boss theme heard during the fights with Kraid, Crocomire and Phantoon. Also, the ominous music that plays directly before battling both Kraid and Phantoon is also heard prior to fighting the mutated Metroid. This, coupled with the fact that the creature can be "defeated", constitutes the Big Metroid as a boss.
|Natural Life Cycle|| |
|Zebes Metroids|| |
|Tallon IV Metroids|
|Aether Metroids|| |
|Phazon Metroids|| |
|Cocoons and Eggs|| |
|Artificial Metroids|| |
|Metroid Hybrids|| |
|Specific Metroids|| |
|Metroid Technologies|| |
|Unused Bosses and Species|
|Metroid: Zero Mission||Crocomire • Ridley-2|
|Metroid Prime||Fireflea • Kraid • IceBoss • Ripper • Skree • Maggot • Kihunter • Sova • Torobyte • Chomper Fish • Experiment 7526 • "Tallon Chameleon" • "Carnivorous Plant" • "Phazon Blastcap" • "Phazon Burrower"|
|Metroid Prime 2: Echoes|| Dark Pirate Aerotrooper • Dark Shriekbat • Dark Sporb • Dark Triclops • Kenobite • Phlogus • Triclops • Zoomer • Sova • Icemite|
Metroid 1.5: Mad AI • Humetroid • Thrash-hunters • Shock beast
|Metroid Prime 3: Corruption||Advanced Pirate Militia • Advanced Shield Militia • Assault Pirate Militia • Assault Shield Militia • Big Metroid • Crocomire • Endocoon • Mantha • Phase Sprite • Phazite Armored Trooper • Phazon Tentacle • Reptilicus-G • Salamander|
|Super Metroid||Bang • Reflec • Stoke|
|Metroid: Other M||Zebesian|
|Metroid Fusion||Geega • Kago spawn • Kihunter hive • Skree|
|3DS Metroid game||Boss Creature|
|Bosses in the Metroid series|
|Metroid||Kraid • Ridley • Mother Brain|
|Metroid: Zero Mission|| King Worm • Mua • Kraid • Kiru Giru • Imago • Ridley • Mother Brain • Ruins Test • Ridley Robot |
|Metroid II: Return of Samus||Alpha Metroid • Arachnus • Gamma Metroid • Zeta Metroid • Omega Metroid • Queen Metroid|
|Super Metroid||Torizo • Spore Spawn • Kraid • Crocomire • Phantoon • Botwoon • Draygon • Golden Torizo • Ridley • Big Metroid • Mother Brain|
|Metroid: Other M||Brug Mass • Fune and Namihe • Groganch • King Kihunter • Mystery Creature • Goyagma • RB176 Ferrocrusher • Rhedogian • Vorash • Ridley • Nightmare • Queen Metroid • MB • Phantoon|
|Metroid Fusion||Arachnus-X • Elephant Bird • Zazabi • Serris • B.O.X. Security Robot • Mega Core-X • Scientist • Yakuza • Nettori • Nightmare • Neo-Ridley • SA-X • Omega Metroid|
|See also: Bosses in Metroid Prime Series|
|Non-hostile|| Aurora Unit 217 • Baby • Dachora • Databot • Etecoon • Fleet Admiral Castor Dane • Fleet Mechanic • Pow • Septogg • Tatori • Tatori, Jr. |
Training Drone • Watchdrone • Work Robot
|Hostiles|| Aazelion • Airthorn • Autom • Big Metroid • Cannon • GMX-04 Halberd-class turret (if provoked) • Polyp • Proboscum |
Puromi • Ring Beam Unit • Ripper II • Samus Eater (Bud) • Seed platform • Unfreezable Metroid • ZipNMEBomber
|Misc.|| Bloatsac • Blueroot Tree (Dark) • Butterflies • Chomper Fish • Durable plantform • Fish • Fungus • Glow Stem • Great Tree |
Massive tentacle • Moth • Parasitic fungus • Protozoan • RedGrass • Sandgrass • Sbug • Scarp • Scatterbug • Tallon fern • Mantha