Forgotten Superweapon

A Forgotten Superweapon is any device that the person or crew had with them the whole time, but they had forgotten that they had. Usually in vampire shows, it's a cross or handy bottle of holy water that was handed to the superhero(ine) early in the show and which she and the audience had long since forgotten until the flash of inspiration hits. The Forgotten Superweapon is very useful in making the audience feel like either they or the protagonists or the writers or all of the above are idiots.

This trope should not be confused with Lost Superweapon, where said weapon has been ignored due to the passage of time and/or its keepers. In contrast, a Forgotten Superweapon will actually be around but forgotten, because the characters have been distracted or the writers hadn't come up with it yet.

If the object in question gets used early in the series and then isn't used at all later, it's Forgotten Phlebotinum. See also Chekhov's Boomerang and Chekhov's Gun.

Anime

 * Mazinger Z: In episode 10 Mazinger-Z shot missiles from its fingers. That weapon never showed up again. It is somewhat subverted, though, since it was not so useful and Mazinger-Z had better and more powerful weapons, so it is likelier than the animators realized it was silly placing missiles in the fingers of a Rocket Punch, and they chose to forget about it and replace them with weapons were not Awesome but Impractical.
 * Uchuu Senkan Yamato involved a ship full of idiots who seemed to forget they had the Wave Motion Gun until the end of each episode. Truly, a show built upon the Forgotten Superweapon. However, this could be handwaved away with the explanation that the ship was almost completely defenseless for several minutes after firing the Wave Motion Gun -- it used so much power they had to wait until the engines came back online.
 * More importantly, the ship is defenseless for several minutes before firing the gun, and completely dependent on its tiny fighter planes to defend it while it preps the gun. If they can just fire the thing without being prevented from doing so, that is usually the end of the fight. Another shortcoming of the Wave Motion Gun is that it is the mother of all BFG's, capable of vaporizing a continent when used at full power, and not every battle warrants that kind of destruction. The first time they used the gun, without entirely knowing what to expect, they accidentally caused a titanic amount of collateral damage and almost fell into the resultant explosion themselves.
 * Likewise, the Super Dimension Fortress Macross had its Macross cannon, which it only ever fired on a handful of the occasions that clearly called for it. That was because the weapon was highly unreliable with technology the crew barely understood in the first place. And that when the fold engine had vanished in the third episode, it took with it the power conduits needed to make the gun work properly in its original configuration forcing a transformation that more often than not threatened to wipe out the city inside the ship!
 * Of course, by the end of the series Macross 7, it was beamspammed.
 * The Big O's Final Stage attack is a chest-mounted cannon that not only blows through an entire city, but required nearly the entire series worth of hints and flashbacks to lead up to its firing. Amusingly, . Pity the series ended with that episode, else he could have worked on that aim (well if the gun hadn't completely turn to scrap after one use, but he might've been able to fix it).
 * The big plot element of The Big O was that everybody had amnesia. So a "forgotten" anything is a trifle redundant.
 * Not to mention that.
 * Thankfully, in the Super Robot Wars games, it worked just fine.
 * Goku's Spirit Bomb in Dragonball Z count during the end of the Buu saga in that Goku had forgotten about it - granted it had been about a decade since he'd used it.
 * Justified since the other two times Goku tried to use the Spirit Bomb to finish an enemy, it wound up being either a partial or total failure (only just managed to hurt Vegeta enough to drive him off and Freeza survived without too much damage). The Spirit Bomb can only be used in his normal form anyway because the Super Saiyan transformations "fill his heart with hate," and it takes a long time to gather the necessary energy, requiring everyone else to hold off the villain for as long as it takes.
 * The title Gundam in Alternate Universe series Gundam X packs the Satellite Cannon, a weapon powerful enough to take out large chunks of the landscape in a single blast. However, it's not forgotten so much as unusable much of the time, since it requires a full moon to power it (the microwave power station has to be in line of sight with the GX to beam the energy down to Earth). In addition, using the Satellite Cannon requires the Gundam X to stand still for several seconds, leaving it defenseless until it finishes charging up. The heroes acknowledge these problems and eventually work out an alternative to the Satellite Cannon.
 * That is, until an upgraded version of the superweapon is provided later in the series, and does not have the apparently most story significant restriction of using the weapon.
 * Then again, an important theme of Gundam X was that the weapon shouldn't be used, showing Garrod reluctant to fire it because of the wholesale slaughter it brings.
 * In Trigun, during the final battle between Vash and Knives, Vash is almost defeated, until he remembers the literal "forgotten weapon" of the Cross Punisher, which he brought with him, but then never used until the last moment.
 * Both averted and played straight in many of Go Nagai's Super Robot series. One of the best examples was Shin Getter Robo, in which the heroes really have no objection to cutting the opponent to pieces with whatever reliable weapon they have out at the time. However, when it comes time to fight Metal Beast Getter G it takes the previously-unmentioned Stoner Sunshine to win the fight.
 * In Yu Yu Hakusho Kuwabara, Yusuke, and the masked fighter fight with three mind-controlled humans for three episodes wrestling with the dilemma of having to kill/harm humans the entire time (they had previously only killed demons). In the end the masked fighter uses a move which removes the mind-control and leaves everyone unharmed.
 * That was intentional. The Masked Fighter realized that Yusuke needed to "grow up" to be able to fight Toguro. Only after Yusuke finally was willing to deliver a killing blow did The Masked Fighter use that technique. Something similar happens later in the series when Yusuke fights the Doctor.
 * Outlaw Star gives us the Caster Gun, a gun that literally spews magical spells with each shell fired, and is also extremely effective against most users of the common-as-crabgrass Tao Magic. However, this is Handwaved away by the guns themselves being increasingly rare and ammo being just as rare in itself (to the point that some types of shells have vanished completely - and no one is making new shells at all).
 * Justified in Science Ninja Team Gatchaman. In this series, the team's ship has the all powerful Fiery Phoenix effect to destroy seemingly any opponent. However, the effect is so taxing and potentially dangerous to the team when it is engaged that they need a good reason to use it. So, the effect is only used in a relatively few episodes and furthermore, it fails to defeat one Galactor mecha at least once and the defeat almost gets the team killed as a result.
 * Used in Yu-Gi-Oh the Abridged Series where Yugi forgets he can summon Slifer the Executive Producer until Bakura mentions it.
 * The Sword of Light from The Slayers might count as an example of this. The weapon is legendary for its ability to slay creatures otherwise impervious to harm, and it is said that the Swordsman of Light slew Demon Beast Zanaffar with a single blow while using it. It turns out to be a Dark Lord from another universe, in the anime at least. When the series begins, nobody knows where it is, until Gourry Gabriev, a wandering mercenary and apparent nobody, reveals that he can actually detach the blade from his own sword... allowing the Sword of Light to manifest its famous blade of solid light. As the Sword of Light doesn't have an actual blade unless it's willing to manifest, he can slot an ordinary blade into it and hide it in plain sight.
 * The Blessed Blade straddles between this trope and Ass Pull when the Sword of Light fails to kill Demon Beast Zanaffar. Sylphiel basically says, "oh yeah, there's the Blessed Blade we can use to kill him. I forgot about it."
 * El-Hazard: The Magnificent World had everyone living under the Eye of God, an ancient super weapon in atmosphere level orbit that's creation was lost to legend and its operations steeped in mysticism and tradition, the damn thing had to be unlocked by three priestesses and operated by two princess.
 * It also has Ifurita, one of the cutest forgotten super weapons in this trope. Compact, devastating and wound up by key.
 * The Third: The Girl with the Blue Eye has Gravestone who/which was presumed destroyed long ago but turned out to be fully operational and both ready and willing to fulfill its purpose.

Film

 * Dude, Where's My Car? plays with this trope and divides it. The superweapon, the, is actually the problem and needs to be turned off, yet the buttons are too small. It's solved with the previously-acquired.
 * Galaxy Quest had the Omega 13 device

Literature

 * Perhaps the most egregious example is the Flaz Gaz Heat Ray, as discussed in Nick Lowe's essay, The Well-Tempered Plot Device:
 * "Everyone knows, I imagine, the story of the Flaz Gaz Heat Ray, perhaps the most outrageous Deus Ex Machina ending in all literature. There the heroes were, stranded deep in an enemy sector of space, surrounded by an entire enemy fleet with the guns trained on them, when the maestro realized all of a sudden he had only one page left to finish the book. Quick as a flash, the captain barks out: "It's no use, men. We'll have to use the Flaz Gaz Heat Ray." "Not -- not the Flaz Gaz Heat Ray!" So they open up this cupboard, and there's this weapon that just blasts the entire fleet into interstellar dust. One almighty zap and the thousand remaining loose ends are quietly incinerated."
 * Subverted in Harry Potter and The Order of The Phoenix:
 * Sirius Black gives Harry a magic mirror in case Harry needs to contact him. Many months/chapters later, Harry really needs to contact Sirius. Harry forgets about the mirror. Lack of communication leads to tragic results. THEN Harry remembers the mirror, too late to be helpful.
 * Harry never knew it was a mirror until after the tragic results, Sirius merely gave him the package, and told him to use it if he needs to talk, but not to open it until he got back to Hogwarts. Harry believes it will be something that will get Sirius into trouble if he does use it, and so never opens it.
 * More specifically, Harry thought that it would be something that would lure Sirius out of his safe hiding space. And he didn't want to be the one to put Sirius into danger .. he fails.
 * THE TIME TURNER from Prisoner of Azkaban could potentially be used to solve any problem and rewrite any timeline. We never see it after the book and film end. In fact, it is mentioned that the Ministry of Magic is the one to have issued it to Hogwarts (to allow a star student to attend multiple classes at once), so it could have been used at any time to thwart Voldemort.
 * ...if it weren't for the fact that (presumably) all the Time-Turners were destroyed during the battle at the Ministry in Order of the Phoenix.
 * Time Turners don't really rewrite the past, you can only act out things that already happened from a different perspective. And that wouldn't help much about Tom Riddle.
 * Time Turners also only turn you back in time - not forward. Even if it was possible to go years back in time to stop Riddle (which, as mentioned above, it isn't), that person would then be forced to live years back to the present, avoiding themselves and everyone they know the whole time, to preserve the timeline - which wouldn't exist anyway, creating temporal paradoxes that would ruin their whole lives.
 * From the Belgariad, the Orb of Aldur is a small stone with literally earth-shattering power. Main protagonist Garion gets his hands on it in the fourth book, and has absolute control over it thereafter, but only uses it directly a couple of times out of many, many dire straights. Why? Because he's too modest, apparently.
 * It's hinted that succumbing to pride and coveting the Orb too much is what lead to the decline of the first Big Bad, and that the same might happen to Garion should he use it to solve all his problems.
 * In The Inheritance Cycle after his battle with  Eragon remembers that he has   which, had he used it, would have let him win easily.

Live Action TV

 * Olaf's Troll hammer in the Buffy the Vampire Slayer episode "Triangle". The weapon was obtained much earlier in the series, and not used through any of the season's numerous crises until they pulled it out in the finale -- where it was shown to be so powerful it could knock around a god (this despite it merely knocking out Xander in its previous appearance).
 * Though, with the abuse Xander survives, nobody is really that surprised.
 * The Dagon Sphere showed up even earlier in the season, but despite knowing that it was designed to repel Glory, nobody actually used it against her until the finale.
 * The possible justification for the Sphere's case is that its introductionary episode already shown Glory finishing off the people who created it with (apparent) minimum effort. Without having the other Superweapons seen in the finale weakening her, the Dagon Sphere is essentially useless
 * And there was that rocket launcher from season 2 that didn't show up again until season 7.
 * Just a few places that hammer could have helped are with the Ubervamps, and over on Angel, someone could have just brought them it when The Beast showed up. Give Faith or Angel that bitch and apocalypse averted.
 * The first time the Mighty Morphin Power Rangers got a new set of (supposedly much more powerful) Humongous Mecha to face their new Big Bad. Their mentor explained that he had been in possession of these mecha the entire time but was saving them for when the Rangers really needed them. This would have been nice to know during a couple of earlier story arcs (though to be fair, the Super Train Megazord from Power Rangers Lightspeed Rescue clearly still had a few bugs to work out during its debut in robot form)
 * The main gun of the Excalibur on Crusade was incredibly powerful, but firing it shut down the entire ship for about a minute due to the power drain.
 * Stargate lives on this trope. Now the superweapons, plebowhatsits, and other toys may not exactly be forgotten, but they tend to be ancient, are occasionally buried, and are usually good for at least one moment of glory. The Ancient outpost in Antarctica springs to mind as an example.
 * Stargate does avoid most of these by introducing inherent flaws or one-time uses into a lot of alien technology. Specifically the Ancient weapon in Antarctica (as well as the chair on Atlantis) was brought up and discarded a few times due to the lack of ZPMs to power it and it's limited ammunition, with the issue finally getting resolved by the Antartica chair's destruction in the series finale of Atlantis.
 * In an interesting subversion, the imminent Wraith attack on Earth did motivate the higher-ups to recall Atlantis back home, even though for a moment it looked like as if they're going to play this trope straight by having the ship unexpectedly break down at the edge of the Milky Way. Fortunately, Zelenka Ass Pulled the wormhole drive out of nowhere.
 * On Heroes, the writers seem to have finally realized that Sylar's power to "understand how things work" is good for more than just stealing peoples' brains. Apparently, it can also be used to understand the show's plot.
 * The writers also forget all of Sylar's acquired secondary powers until convenient.
 * One of the worst cases was where Sylar decides to go on a mission to investigate if Arthur is really his father. Now, the simple solution would be to use his super brain to realize that people in the real world have this thing called a "paternity test." Also, everyone's DNA on the show is already on the national database, because that's how Mohinder found them, making this rather straight forward. Instead, he decides to go on a mad hunt for more super powers, in the hopes that he will find one that will give him the answers he needs. By sheer coincidence, the next lady he finds reveals that she's a living polygraph. Mystery solved.
 * The same goes for Peter, back when he still had more than one. Hell, the second season volume could be named this as Peter never uses any of his powers after dropping his amnesia, except as the Idiot Plot demands.
 * Claire/Adam both have Jesus blood, which is so powerful can bring people back from the dead who've lost large chunks of their brains. Apparently the writers never considered the ramifications for such a device, and conveniently ignored it later on.
 * Molly has the power to locate anyone on Earth. Molly sees Sylar as the boogie man, because he murdered her parents. At the end of season 1, Sylar disappears from the scene with a trail of blood leading to a sewer. Yet she never once thinks to use her powers through season two to confirm that he's really dead.
 * This is especially maddening at the end of season two, when Sylar kidnaps Molly only to be rescued by Elle. Sylar narrowly escapes, and no one thinks to use Molly in order to chase after him.
 * This continues even into the alternate volume three, which can be scene on the DVD. Elle is still on the trail of Sylar, who is accumulating more and more powers. Again, despite the fact that Molly has the power to track Sylar down.
 * Star Trek: Voyager collected dozens of examples of alien technology and weapons from various encounters, from hand weapons better than theirs up to superweapons. None of it ever appeared after the episode they captured it.
 * Star Trek: The Next Generation had an interesting twist on this with a Forgotten Vulcan Superweapon that amplified its user's telepathic powers until it could effortlessly destroy any foe. Picard and Riker wind up attempting to keep it from being re-assembled.
 * One episode of The Unit had Alpha Team trying to disable a bomb which will set off nuclear material in a train. The bomb is under an overpass on which the train is traveling. However, the team forgets that they have "national security" command over the entire infrastructure of America, so the train conductor isn't told to stop the train until it's almost too late.
 * Supernatural introduces a handgun, forged by Samuel Colt himself in 1835 that has the ability to kill any demon with one shot. Originally, The Colt was limited by the number of bullets it can fire, but Bobby Singer forged new bullets, thus solving that problem. And after an altercation with, it is never seen again.

Tabletop RPG

 * In Warhammer 40000 mankind has lost much of the technology created during the "Dark Age of Technology" (or Golden Age if you ask the techpriests), resulting in all kinds of forgotten superweapons. Some of most powerful spaceships and battle titans kinda fit to this trope as the technology to make new ones has been lost or it takes centuries to build one. It is also hinted that the Necron tombworlds hide some truly powerful weapons that will be activated if the Necrons encounter heavy enough resistance. It can be assumed that these are more powerful than the weapons they currently use, which is to say something as one of the deadliest Necron weapons encountered so far generates what is essentially a tiny star, capable of incinerating vast swathes of the battlefield in a single blast.
 * The new Space Marine Codex brings in one such more powerful Necron weapon-the World Engine, which wrought havoc across a subsector before being stopped, at the price of an entire chapter of Space Marines. It's hinted, however, that there are more World Engines waiting the call to awaken-and possibly weapons more potent still...
 * Nuclear Weapons. Sure, they aren't powerful enough for Battlefleet Gothic but WMD are hardly used in situations where they would be incredibly useful. There are occasionaly reasons why they can't be used (don't want to hit the agri-world, city more valuble under our control, don't want to give them ideas), but generally they aren't even considered by writers.
 * They still get a passing mention with the Death Korps of Krieg. A world turned into a desert by a 900 year campaign of nuclear purging.
 * Uh, WMDS are used all the time, 'Atomics' are considered inefficient, instead things like Virus and 'Melta' (Fusion) bombs are preferred. Their availability is limited, though, and their use requires the certification of segmentum command.

Video Games

 * In Metal Gear Solid, the small card that you've been carrying around the entire game without really knowing the purpose of is the only way to activate the Humongous Mecha without the password.
 * appears to have become this by the time Metal Gear Solid 4: Guns of the Patriots happens.
 * At the end of Zork: Grand Inquisitor, Dalboz mentions that now would be a good time to use a spell that came with your spellbook and hasn't been used yet in the game. Casting the spell restores magic to the land and ends the game.
 * In a way a literal inversion, as the spell was written in the book backwards and needed to be magically turned around in order for it to work properly.
 * Shiki's battling against Nanaya, his manifested nightmare of becoming a murderer, in Kagetsu Tohya never goes well, since Nanaya Shiki is simply a much better fighter than Tohno Shiki. It takes a while for Shiki to remember his one advantage: Nanaya doesn't have Mystic Eyes of Death Perception. . He then proceeds to forget his eyes again until halfway through his fight with.
 * Homeworld Cataclysm has the Siege Cannon. Homeworld 2 has both the  and.
 * In Super Robot Wars Advance, the Original Generation Super Robots' final attacks can be explained away as Axel or Lamia taking that long of a time to figure out that they could overclock their rides that way. It takes a bit of research and analyzing schematics to realize that the Ash Saviour's extra armor plates are actually Attack Drone pairs. However, there is no excuse for not figuring out early on that that big, folded-up cylinder mounted on the Laz Angriff is anything but a really big cannon.
 * In Starcraft II, throught the game you have to obtain several Zel'Naga artifacts. These

Web Comics

 * Bob and George: Bob reminds George, after rescuing him, that he could have used his superpowers to escape. George blows up the fortress
 * Tweaked, here. (Answer: it broke.)
 * Schlock Mercenary has "Discontiguous Particle Acceleration System". As the team's Pyromaniac figured out, a weapon that "was built before teraports and too big for wormgates [...] not sharing the system with anything worth attacking or defending" should be a "Hyperspace Death Ray". It wasn't used on account of . Tagon's Toughs accidentally prevented an attempt to reclaim it by the proper owner's successors, then the new owner (who knew what it is and who he deals with) quickly moved and the gun to "undisclosed location" as soon as possible, after which let Toughs witness the test firing as a bonus.

Western Animation

 * Combat in Megas XLR is built around the Forgotten Superweapon, with many of the trump cards apparently winking into existence as needed, never to be seen again after their use. The pinnacle of the lot is a weapon that causes the title robot's hands to burst into flames, activated with a button marked "Five Minutes 'Til End Of Episode." The one in "Dude, Where's My Head?" even had the computer raise its eyebrow.
 * Subverted by the "Voltron Sword Thing", which was first a combo move, then became a button.
 * Adventures of the Galaxy Rangers had the Scarecrow, a living weapon buried and dormant for centuries, until a new farming colony is built on the old battle site. Terror ensues.
 * Transformers Animated has, who could have been used as soon as they had some AllSpark fragments. Granted, the series is a mild aversion of No Endor Holocaust, so they probably just didn't want to escalate a battle if they could help it, but that doesn't explain why they didn't at least bring him back online.
 * To be fair to the other Autobots and Sari, Ratchet seemed to be the only one who knew about Omega Supreme, and not even he seemed to know for sure that attempting to reactivate him would actually work.
 * The Great Gummiscope in Adventures of the Gummi Bears.
 * Voltron never formed Blazing Sword until after the Ro-Beast and Voltron had stomped half the countryside flat and Voltron was getting its ass handed to it on a big Roboplatter. However, this was for a very good reason: Voltron could not defend itself while wielding the sword, so it had to fight until the robeast was incapacitated or gave them an opening. In an early episode, Voltron Force faces a new Juggernaut robeast built by King Zarcon, not Haggatha's sorcery. They come out with Blazing Sword already formed, but get roundly trounced. For three days, the Royal Army holds off the monster while Voltron trains, and in a huge battle, the individual Lions beat down the robeast until it can't fight back, then form Voltron, blast it a few more times for good measure, Form Blazing Sword, and dispatch it.
 * This was parodied in an episode of Robot Chicken were it went through a dance contest against a Ro-Beast and lost, but then just used the sword while it was laughing at their defeat.