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Forgotten Phlebotinum
"The issue in an ongoing series is once you've done it [used Time Travel] and it wasn't a fluke, it's like you've shown that one of your characters got Superman powers. And then in the next episode when a building is about to fall over on someone, Superman's running around in circles saying "Oh no what do we do? Frig frig frig" and the audience is sitting there, furrowing their brows, one hand on their chin."

A situation, most common in Speculative Fiction, where an amazingly useful power or device is revealed in one episode, and would be amazingly useful in later episodes, if it weren't for the fact that nobody seems to remember it. Sometimes the power or device is remembered under circumstances where it proves mostly useless, but not remembered when it would do any good.

This trope does not necessarily denote bad writing. It can be (as noted in the Order of the Stick example) convenient writing instead. If the protagonists have some piece of phlebotinum that makes them invincible or at least very hard to so much as injure that is both reliable and accessible, vast numbers of plots have to be thrown out the window. Some would call this unwillingness to change the Status Quo and then adapt to the new order of things "lazy", but when one is working on a regular series, changing the status quo (interesting though it can be dramatically) is not something to be done lightly. When it's a Shared Universe this is even more pronounced.

Larry Niven is extremely critical of this trope, and coined Niven's Law, which states that once a technology or discovery has been introduced into a fictional setting, it must continue to exist in all chronologically later stories in that setting. The secret may be lost for a variety of reasons—society enters a dark age, the discoverer deliberately covers it up, or there really were No Plans, No Prototype, No Backup—but Niven would maintain that this smacks of lazy writing and is best avoided. At the very least, the precedent that such a machine is physically possible in the setting must be maintained—which makes it likely that older, Higher-Tech Species will possess it even if it never became prevalent in the protagonists' society.

This is for powers or devices that are forgotten in general. Something which the character does use a lot and only is forgotten this one time is an example of Forgot About His Powers. If the device is remembered, but there's some contrived excuse as to why it isn't available or won't work, that's Holding Back the Phlebotinum or It Only Works Once. Not to be confused with We Have Forgotten the Phlebotinum. If they (finally!) remember to use it in the end, it's a Forgotten Superweapon. When it's not forgotten and is used in a later episode because a writer wants to acknowledge continuity, it is Chekhov's Boomerang.

Can be related to a heroes version of Never Recycle Your Schemes.


Examples:

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    Anime and Manga 
  • In Cowboy Bebop, the crew seems to conveniently forget that they have a nigh-omnipotent hacker on board who could take over other ships at will in her initial appearance but never, ever does that again, even though that would not exactly be the least effective way to catch their bounties. It was particularly bad in the episode where the villains are immobilizing ships through a computer virus. Gee, if only they had someone on board who could counter that...
  • In Digimon Adventure, there were several instances in which Gomamon's Marching Fishes technique could have come in handy, especially since he was seen in the first episode carrying the entire group down a river on the fishes.
  • This is not uncommon in Doraemon. There are several predicaments that Doraemon and co. face that one of his gadgets that have been mentioned in previous episodes could have easily get them out but for some reason Doraemon seems to have to use the gadget that was introduced in episode they were in. One the early gadgets of the week (chapter 54, "Lies Become Truths") was a beak-like toy which one could wear, and anything uttered while using it will be spontaneously proven as fact. Nobita lied that his father can shatter a huge rock with his bare hand, and then he can do it with ease. Quite frankly this should have make any other gadget Doraemon had introduced, or will ever introduce, completely and utterly obsolete. It was never mentioned again ever since. Particularly frustrating in Doraemon feature films and volume-length comics, which featured life-threatening situations.
  • Mazinger Z: Often it was played straight. Many times Dr. Hell came up with a Mechanical Beast equipped with a weapon put Kouji or Mazinger-Z in a serious disadvantage: Gromazen R9 shot an acid could melt Aphrodite A's armor (that was made of Japanium, although it was less tough than Mazinger Z's), Kingdan X10 projected mirages, Holzon V3 set earthquakes off, Jinray S1 flew at Match 5, Aeros B2 could absorb Mazinger's attacks and hurling them back, Desma A1 caused hallucinations, Gumbina M5 was nearly invulnerable... and they were not used again. However, sometimes Dr. Hell reused and improved some strategies or weapons, or deceived the enemy in believing he was using the same trick.
  • Kakashi from Naruto. Turns out he's had the Mangekyou Sharingan for about 18 years. Sure would've been useful fighting Itachi and Orochimaru! Granted, it took years for Kakashi to build up enough chakra to use it by the time of Shippuden, perhaps explaining why he fainted upon its initial activation.
  • Sailor Moon:
    • In the first episode Sailor Moon's hairclip things (on her odango/buns) can magically allow her to hear people in distress. This comes in handy, as she hears her best friend Naru being attacked by the Monster of the Week and goes to save her. This power is never shown again in later episodes, even though it would probably have come in handy. Similarly, in the first chapter of the manga, the costume included a mask in which she could see the monster attacking Naru by looking in the goggles. The goggles were quickly phased out in the manga, last seen in one transformation sequence where Usagi discarded them as she transformed, though why this happened was never explained. Considering that the monsters of the week/chapter were usually close by anyway, this power wasn't really that necessary in retrospect...
    • Another forgotten ability was Sailor Moon's disguise pen. It was commonly used early in the series, but forgotten during R and appeared only once later off screen, to explain why Venus was disguised as Moon. This may have been due to the lack of need for Usagi to actually use her disguises in later storylines as she gathered a team of fellow heroes and many of these disguises often appeared superfluous to the plot anyway.
    • Sailor Moon used a special attack, "Moon Tiara Stardust", in episode 5, to heal a group of transformed humans. She never used this again, despite it possibly being useful in many storylines, though she eventually acquired the Moon Stick which had the same abilities. This is likely because the former attack never showed up in the manga, while the latter item did.
  • Tekkaman Blade gives us the Hi-Coat Voltekka, an upgrade to Blade's Voltekka. It's used once in it's introduction episode to defeat Evil and then again three episodes to shoot down a nuke. Then the time skip happens and it's not seen again.
  • Tengen Toppa Gurren Lagann: The Gurren Lagann is equipped with a powerful Deflector Shield, which stops Combat Pragmatist enemies from attacking it in the middle of its formation, as well as stopping any powerful attacks thrown at it. It only appears in episode 3 and is promptly forgotten for the rest of the series, where it could have been very useful. (It reappears in the Compilation Movie, however.)
  • YuYu Hakusho
    • In early episodes Hiei has telepathic abilities and has the ability to transform into a more powerful demon form, which eventually disappeared. The demon form was seen again in the second movie, but it seemed less powerful than Hiei with the Black Dragon Wave. The telepathic abilities such as hypnotism still appeared in the show and manga near the ending.
    • Kurama has a number of really nifty tricks that show up only once, when they would have been incredibly useful at other times (such as during Round 3 of the Tournament), like the smokescreen and the Petals and Thorns attack. Many of the techniques he can use are dependent on which plant seeds he has on his person at the time, so it's possible he only has a limited number of different seed types on him at any given time.
    • Kuwabara showed in his first fight in a while that through training he's gained the ability to create a second Spirit Sword, manipulate his sword to extend and bend to hit opponents from long distance, and during his fight against Elder Toguro, create a colossal tennis racket-hammer thing out of the same energy; all of these abilities are never used outside the fight they were introduced in.
  • There are a number of things in A Certain Magical Index that only come up once and are discarded once Touma or another hero defeats them. The Level Upper program from A Certain Scientific Railgun, for example, is a noise file that increases a listener's power level before putting them in a coma, in which state they can be used as an organic computer for the controller of the network to make use of all their powers—this would be absolutely perfect for the Sisters, but it's never brought up. Though in the case of the Sisters, Level Upper is related to, and derived from, the Misaka Network, which is utilised in a similar manner to create Fuse=KAZAKIRI, an artificial Angel as strong as a Level 5. Also, Level Upper, as it presently existed, resulted in comas, which is bad, and an uncontrollable menace, which is worse. The Misaka Network is the better version, and Level Upper is shown in the prequel sections of Railgun in order to lead into that.
  • Yu-Gi-Oh! 5Ds:
    • Yusei's Turbo Warrior would have been immune to the effects of the Meklord Emperors and likely would have been useful, but Yusei conveniently forgets that he has Turbo Warrior whenever a Meklord Emperor hits the field.
    • An even better option that he also had was Dragon Knight Draco-Equiste, a Fusion Monster, meaning that the Meklords couldn't equip it even if its effects were negated. Draco-Equiste only ends up being used in 1 duel.
  • In Super Dimension Fortress Macross, we see that the Humongous Mecha piloted by humans have head-mounted cannons - that got used exactly four times during the entire show. Only twice as a weapon - both of the other times they were used as cutting tools.

    Comic Books 
  • Silver Age Superman's lead-glass suit. It's flexible, bulletproof, doesn't cover up the "S", and is impervious to kryptonite radiation. It shows up in one issue.
    • Superman: The Animated Series uses it, but makes it even more useful by turning it into an effective (if short-term) spacesuit (Superman can survive in a vacuum, but can't breathe in one, in the animated series). It is, however, noticeably more fragile than Superman himself, so while he uses it often, he's not reliant on it.
    • The suit reappeared for a story arc of Superman/Batman somewhat recently.
    • The Silver Age had tons of Forgotten Phlebotinum. For example, there is Action Comics #252, an issue otherwise better known for being Supergirl's first appearance. In the lead-in story, though, Superman is being menaced by kryptonite, and he escapes by melting it with his heat vision, at which point he learns the liquid kryptonite is no longer harmful. (In a real head against wall moment, he even says that it's because when items change their state, they lose other properties, like how ice, when it melts into water, stops being cold. Superman forgets that liquid kryptonite is harmless to him thereafter, and in fact, liquid and gaseous kryptonite are shown being harmful to him in later stories. So maybe he found the only chunk of kryptonite in the universe that would be harmless to him if it were liquid.
    • In those days, Superman also collected all manner of exotic gadgets in his Fortress of Solitude, in addition to all the Kryptonian gizmos in the Bottle City of Kandor. Generally, DC Comics's Superman continuity cop (and world's biggest Superman fanboy) E. Nelson Bridwell was the only writer who consistently remembered what a fantastic array of machines Superman had access to.
  • Shows up in one of the many Avengers stories (the relaunch with Kurt Busiek). Justice, sidelined with a broken leg, goes on an Archive Binge and realizes that the best way to defeat an Adamantium robot on a homicidal rampage is with Antarctic (type B) Vibranium (AKA Anti-Metal), a metal that somehow destroys any other metal within range when exposed to the air. Fortunately, the Avengers destroyed an AIM base with stocks of type B vibranium four or five issues previously; but in all the long history of Ultron's rampages, some of the finest minds (Stark, Pym et al) in the world never linked the "really tough metal" and "destroys metal on contact" dots together.
  • One serious cause of this in comic books is the variable access to technology between different books even where there shouldn't be any. Batman operates in a much lower-tech universe than the rest of The DCU, despite hanging out with Superman in the Justice League half the time. This becomes wall-banger material when you consider Barbara "Batgirl" Gordon, shot through the spine and confined to a wheelchair for the rest of her life. If this happened to Lois Lane, you know Superman would scour the galaxy for a cure and have her on her feet by sunset, and that's before considering the number of people on the planet who have healing powers! Call in a favor, Bats, you've earned it! But, if the characters in the DCU, or any other standard comic book universe, actually treated the technology and superpowers they encounter daily in a realistic fashion, half their problems would be solved before they turned into interesting stories.
    • In the case of Barbara, she explicitly refused to seek a cure from her various superpowered contacts, preferring not to benefit from medical technology not available to the everyday populace. There's no good reason that Krytonian/Martian/Thanagarian/Amazonian technology couldn't be made accessible to the public, making this a case of Reed Richards Is Useless. While not available to the everyday populace, it turns out the best cure after all was a reboot.
  • X-Men: Rogue can't have a relationship with anyone due to her powers. Gambit's mutant powers used to allow him to touch her without an issue, which has since been forgotten. In addition, there have been numerous items that temporarily disabled mutant powers, many of which have been captured by the X-Men, but are never mentioned in relation to this issue. At least one writer has admitted that there is no in-universe reason someone like Forge couldn't whip up a gadget to temporarily nullify Rogue's powers whenever she wanted, but that would make her character "less interesting".
  • Spider-Man:
    • Peter makes a gas mask for himself that is completely concealed by his Spider-Man suit; he uses it once and never again, even though he is regularly hit with gas attacks several times during the early run of the comic.
    • The loathed One More Day storyline. Aunt May is dying (well, she's only been in her mid-80's for a few decades now, but she was actually injured). Subverting this trope, Peter scours half the mainstay Marvel cast looking for someone that can heal her. Playing this trope straight, nobody can. There's very, VERY thinly implied instances where it's the fact that she's already so old and frail that conventional medicine can't heal her, but considering the fact that those who he approaches include the X-Men (who had no fewer than 3 people at the time whose powers could explicitly heal any wound), Reed Richards, and Doctor Strange - who is both the Sorcerer Supreme and a former neurosurgeon, there's no reason that SOMEONE couldn't have helped him before he ended up letting Mephistopheles wipe out the entire history of his marriage in exchange for Aunt May's life.

    Fan Fic 

    Films — Animated 
  • A rare villain example in The Nightmare Before Christmas: Oogie Boogie has the ability to suck in everything like a gigantic vacuum, which is how he recaptured Santa and Sally. He never thought to use this in his battle against Jack Skellington.

    Films — Live-Action 
  • In Star Trek: First Contact, the invading Borg are able to create a "temporal vortex" to travel back in time to the 21st century. At the end of the movie, the Enterprise is able to easily recreate this effect to travel back to their own time. This method of time travel seems easier and much safer than the other established method of slingshotting around a star at warp 10, but it's never mentioned again. And if the Borg posses the technology to Time Travel at will, why not use it to undo all their failures? In particular, they could have averted their Hopeless War with Species 8472.
  • At the end of Star Trek: Nemesis, all the transporters on the Enterprise fail after Picard is beamed over. Their only recourse is to have Data jump over and use a never-before-seen one-person mini-transporter badge to get Picard back and then die with the enemy ship himself. Everyone seemed to forget the shuttles have their own independent transporters. Also, the shuttlecraft themselves; they could just send Data over carrying a spacesuit and have him jump through the forcefield with Picard back to the shuttle.
    • Insurrection and Nemesis has the Captain's Yacht, a large auxiliary starship (attached to the underside of capital ships) that was designed for both The Next Generation and Voyager, but was never used in either series. Despite many situations where a craft like this could be useful (as it could carry more crew members, have a larger cargo area and generate tachyon bursts), the craft wasn't utilized until Insurrection (where the main cast go down in the yacht to deliver weapons to the Ba'ku) and Nemesis (where Picard arbitrarily decides to take it down to the planet where B4-4's parts are located).
  • In the 2009 Star Trek reboot and its sequel Star Trek Into Darkness, there is a Laser-Guided Amnesia subversion of this trope. In the first movie, the Spock from an alternate future introduces "transwarp transporting", which works across interstellar distances. He shows this to the younger version of Scotty, and uses it to send him and Kirk to the Enterprise, which is currently traveling at warp speed. In the second movie, Harrison uses it to beam from Earth to the Klingon homeworld Qo'noS. This demonstrates that knowledge of the technology did leak out, but is now exclusively used by the villains, with the heroes seemingly no longer remembering how to do it, even though they were the first to learn how it works. This overlaps with the Reed Richards Is Useless trope.
  • The "throwing 'S' shield" in Superman II. During a fight which occurs just before the climax, Supes rips off a copy of the 'S' emblem on his chest and uses it to temporarily incapacitate Non (one of the escaped Kryptonians). It's never explained how Clark does this, and he never uses it again in the following films. It sure would have come in handy against the evil Clark or Nuclear Man, even if it was a cheap-looking effect.

    Literature 
  • In Inheritance Cycle Eragon learns that Brom's ring contains a massive store of magical energy, enough to rip castles apart. He keeps outright, explicitly, forgetting that he has it.
  • The Grey Griffins books forget their phlebotinum all the frigging time. All the time. Other times they hold it back. Max can sense portals and enter them... wait, now he can't, except when he suddenly needs to warp into one much later. Max has a pet "spriggan" that he cares deeply about. Where'd it go, and how come neither Max nor the book cares? You get the idea. Contributes to the randomness of the plot.
  • A very subtle version of this happens in L. E. Modesitt's Spellsong Sorceress cycle. In the first chapters of the first book, a spell is cast that teleports the main character in from Earth. It's implied that although the lady casting this spell isn't a very strong sorceress, she can still send people to locations halfway across the continent with a bit of help. This use of magic is never mentioned again, despite the fact that it would be tremendously useful in a variety of circumstances.
  • Harry Potter:
    • Sirius' two-way mirror, which is a magical walkie-talkie. In Harry's defense, he was never told exactly what it was, and swore never to use it for fear it would cause Sirius to come to Hogwarts and get arrested and/or killed. It still qualifies as forgotten phlebotinum, however, because even after Harry has gone through great risk to speak to Sirius through Umbridge's fire, it didn't occur to Sirius to tell him "Next time, use the mirror I gave you." which would have saved his life.
    • In Harry Potter and the Deathly Hallows, Harry and his friends escape from the Malfoy mansion. At one point, Harry ends up with three wands in his hand, which he holds bundled together. When he attempts to Stupefy someone, his target is "lifted off his feet by the triple spell." However, every character is usually content to wield a single wand. No one habitually Spellotapes a few wands together for extra blasting power, no wandmaker designs multi-core wands - nothing of the sort.
  • Science Fiction author Larry Niven coined "Niven's Law," which states that once a technology is introduced into a setting, it must continue to be present in all later stories in that same setting.
  • In the Star Trek Novel Verse, the phase-cloak seems to go through this a lot. After its introduction (and successful use) in an episode of Star Trek: The Next Generation, it's largely ignored by the books (as well as later TV series). A short story in a Star Trek: New Frontier anthology eventually suggested the prototype was destroyed soon after the episode. By the time of Star Trek: The Genesis Wave, the Romulans are making use of the technology again, or something very much like it, but then it drops off a second time, and when Star Trek: Titan comes round no-one's using it. Finally, in the Star Trek: Typhon Pact series, we're explicitly told the Romulans have finally perfected it.
    • At least in The Next Generation, it was mentioned that the Federation had negotiated away its right to use cloaking technology in a treaty with the Romulans, making the Federations research into the phase-cloak illegal (i.e., a treaty violation that could lead to war with the Romulans). The episode showing the Romulans were working on it themselves showed that it was giving them trouble, and the illegal Federation project Riker had been a part of had not ended well either.
  • The Grav Lance in the Honor Harrington series is a key plot point in the first book, and is then never mentioned again. Considering how much other technology advances over the course of the books (about 20 years in universe), you'd think they could have worked out the glitches of a weapon that can one hit the shields of any size of ship, up to and including a superdreadnought. Its sponsor lost favour, and its debut performance generated massive bad feeling amongst the other powers-that-be, so it could be deliberately kept out of action.
    • The Grav Lance required the ship using it to be at extremely close range to its opponent, and the energy requirements meant that the ship's usual defensive weaponry had to be gutted. While it did work as advertised, the ship was nearly destroyed in the process. Still, it was only a prototype, and could have been refined to be less dangerous to its own crew.
  • The Alliance Rune in The Mortal Instruments. After City of Glass it's never used again, even when Shadowhunters and Downworlders are going into battle right next to each other.

    Live-Action TV 
  • Star Trek: The Original Series was notorious for this.
    • In "Plato's Stepchildren", the Enterprise crew discovers kironide, a drug that gives people psychic powers. Why wasn't this made a standard part of the medical kit, even if it is too dangerous to use all the time?
    • Then there was the subcutaneous transponder, which gave the ship the ability to lock onto and beam up the landing party if they were out of contact. Its actual purpose in the plot was to give Kirk and Spock a Cool Escape, rather than pull the whole trick-the-one-inept-guard bit again. Despite the number of times they were separated from their communicators, the thing was never seen before or since. You'd think it would be standard issue.
    • The original series did this many other times with Scalosian water ("Wink of an Eye"), and spores that can regenerate lost body parts, restore the human body to perfect health and give immunity to radiation ("This Side of Paradise").
    • The movies introduce the Genesis device (a form of instant terraforming that may bring people back to life as a side effect), which is so much further advanced than anything the Federation possesses before or since that it might as well be magic. The planet it creates disintegrates within a couple weeks, but surely there would be a way to work the kinks out within the next century, and the research that went into it could at least be applied to other projects, like a handy-dandy anti-Borg weapon. But in The Next Generation and Deep Space Nine terraforming is a long and arduous process that yields modest results. Ultimately it's a case of No Plans, No Prototype, No Backup; every copy of the schematics is lost and everyone who knows how to make it is dead. Given that the Klingons considered it a treaty-violating planet killer superweapon, there was probably political pressure not to rebuild it.
    • A major problem with Star Trek: The Animated Series being considered canon is that the enormously useful life support belts never appear in any later Trek works. The belt surrounded the wearer with a glowing forcefield within which breathable air was provided. The real reason was that it was cheaper to animate a glowing outline than it was to draw spacesuits on everyone.
  • Star Trek: The Next Generation also indulged in this far too often.
    • Consider the "dimensional inverter" used in the episode "The High Ground", that could transport things straight through even a Galaxy-class starship's shields (or any other shields) without trouble, but had a cumulative and lethal side effect on people who used it repeatedly. And while that's obviously a sane reason not to use it in normal service, it does nothing to explain why they didn't use it for, oh, one-way trips by inanimate objects straight through enemy starship shields... objects like armed anti-matter warheads, for example. (Or as a Plan B for when crew members are in danger on the planet but can't be beamed up due to an attack on the ship that requires them to keep their shields up or a Negative Space Wedgie that blocks the beam).
    • Or the episode "Lonely Among Us" where the transporter brought the dead back to life! Although it's possible that this was only feasible in that one case, since the person's consciousness had been converted into energy by the being that had possessed him. Still, the episode seems to imply that they can always rematerialize a previously saved version of a crewmember.
    • The Galaxy class has Saucer Separation capability because the Saucer section contains the civilians, laboratories, families, etc., while the lower section contains the warp drive and primary weapon systems. It allows the civilians to be moved out of harm's way if the ship has to go into a firefight. Saucer separation was used twice in the first season of the show, but after that it was forgotten and only sometimes referred to, just to drop the idea afterwards. It was, however, used in one of the movies. The Star Trek: The Next Generation Technical Manual explains in a footnote that the writers never forgot about the Saucer Separation capability, and originally intended to use it as a fairly standard maneuver whenever the ship expected to go into trouble. However, what they discovered is that depicting the separation on screen and showing crew moving to the other set just took too much time during the episode to show fully, and not doing so was too jarring of a sudden transition. Hence, they used it sparingly (if at all) for pacing reasons.
    • "Hero Worship" has Geordi connecting the shields to the warp drive to more than double their strength. Never mind the other hundred times when this would have been useful.
    • The transporters were remembered. The shuttles were (usually) remembered. What was not usually remembered was the fact that the shuttles have independent transporter units of their own, separate from the ship's (they didn't in TOS, but TNG established it).
    • "Who Watches the Watchers" has Troi and Riker implanted with subcutaneous communicators, allowing two-way communication between themselves and the Enterprise, which only the ground team can hear. Naturally, this technology was only ever used four more times over the course of the entire franchise, despite existing as early as the 22nd Century according to Star Trek: Enterprise.
    • In "Rascals", a transporter accident turns some crew members into young children. Inconvenient at the time, but the staggering medical implications are never explored. The entire plot of Star Trek: Insurrection could have been avoided if they figured out how to just zap people back to their twenties every time they got north of, say, fifty. Considering that they were able to reverse-engineer the accident well enough to return the crew members to their original age in the space of one episode, it shouldn't be too hard.
    • Or how about the fact that Dr. Soongh spent decades trying to hook Data up with a positronic brain capable of sentient thought, while Geordi did the same thing with one poorly-worded request in the holodeck. Oh, they tell Moriarty that they'll look into how and why it happened so they can try to figure out a way to let him leave the holodeck... and then promptly forget all about it until he shows up again seasons later.
  • Star Trek: Deep Space Nine came up with a holographic communications array, installed it on the Defiant's bridge and Sisko's office, used it all of three times and forgot all about it. Other than looking cool and saving some money on blue-screen usage, it really served no purpose at all.
    • They also had an easily replicable gun capable of shooting through walls (a combination of x-ray goggles and micro-transporter). Like SF Debris mentions, that weapon could have been useful on many occasions.
  • In Star Trek: Voyager, the crew conveniently forgot several gadgets that could have gotten them home, or at least closer to it:
    • Q Jr, depowered, retains enough Q knowledge to use the Delta Flyer's [insert Techno Babble here] to create portals, without any unpleasant Star Trek Shake-inducing side-effects that we saw. The crew could have done whatever it was that they did and gotten home via a series of portals, or at least - as was often the case with Voyager's non-deadly shortcuts - shaved a decade or two off their trip before the Applied Phlebotinum gave out.
    • In "Threshold", where the otherwise successful test of an experimental transwarp engine turns Janeway and Paris into newts. An imposing side-effect, to be sure, but one which they have cured by episode's end, leaving them in possession of a magic new transportation technology which could get them back to Earth almost immediately, and a cure for its inevitable side-effect. So rather than using it to return to Earth, or even send a message back to the Federation (this was before the Federation discovered that Voyager and her crew had survived), they roll end credits and never mention it again. Even the producers try to forget that episode, so it's no surprise the characters forget it too.
      • Even ignoring the lizard-fication, "Threshold" mentions that the experimental shuttle's computers were jam-packed with helpful navigation aids and maps—which are never mentioned up again.
    • Through contact with a vengeful alien, the crew gained access to the quantum slipstream drive, which could have literally taken them home inside a hour. After the first attempt to replicate the technology was deemed too dangerous to use again, they improved it. This version worked for three minutes, then would have crashed the ship if not for Time Travel fixing. It's discussed, at length, that the technology is stable for those three minutes. No one ever considers just running the drive for two minutes at a time, and they never use the technology again.
    • Seven of Nine once brought Neelix back from the freakin' dead after several hours via (what else?) nanoprobes. Apparently, the technology must only work on main cast members. Only that one time...
    • Throughout the series, Voyager manages to cut a collective 30-50 years off their journey. As the (non-altered) future of the series finale "Endgame" shows, after the crew ignored the Borg temporal node, they supposedly spent the next 26 years merrily skipping along on their way to Earth without the aid of any of the aforementioned technologies. It's like the crew just gave up and decided to go the traditional way, even though Janeway wouldn't have hesitated to use an advantage if one presented itself.
    • The complaint about the Nemesis movie applies to several Voyager episodes as well— the show gives a reason ship-board transporters won't work, but they neglect to explain why they can't use the shuttle's independently-powered transporters.
  • Buffy the Vampire Slayer:
    • One episode had the minion of the First Evil falsely claim he had kidnapped a proto-Slayer. Nobody thought of using the "detect proto-Slayer" spell discovered a few episodes before.
    • The issue of the Adjoining Spell from the end of Season Four. Arguably the most powerful spell seen in the entire series, although with the drawback of causing the spirit of the First Slayer to try to kill everyone involved in their dreams.
    • At the end of Season 5, Buffy uses a hammer that (somehow) allows her to pulverise Glorificus, a literal Physical God that had shrugged off absolutely everything that was thrown at her before. Said hammer is never seen or mentioned again, despite how useful it would have been against, say, the Turok-Han or Caleb.
    • Similar to the flamethrower instance from Angel mentioned below, in one second season episode Buffy kills a random mook vampire by shoving a burning torch/brazier against its chest, which causes it to go up in flames like it was made of straw soaked in gasoline. Given how the series occasionally spiced up vampire-killing up with decapitation or holy water, it's a small wonder fire didn't come up more.
    • Anya's power center necklace. When she turned demon again, it seemed she never needed it.
    • Discussion here regarding the lack of willingness to use an established spell that returns a vampire's soul. There are consequences and complications, but the fact is that they are never discussed and the protagonists happily go around slaughtering vampires as if this ritual doesn't exist.
  • Stargate SG-1 usually avoids this, with plenty of Chekhovs Boomerangs shown years apart, but it still has its examples.
    • Kull Warrior Armor. That stuff shrugs off claymore explosions, and is light enough to wear, yet while Vala is able to get her hands on a suit and capture a starship — a United States starship, no less, so you'd think they learn — with it, the US military doesn't even seem interested in it. Plus it looks really Badass.
    • Season 3, "Past and Present": They discover a drug that reverses the effects of aging. Next episode, it's forgotten.
    • Atlantis is on Earth. Atlantis. The Ancient city-ship with sensors that are capable of picking up even cloaked ships in practically one third of the galaxy away from wherever it happens to be. The database of which contains truly obscene amounts of information on Ancient technology. And yet not only do they barely touch on the database in Stargate Universe (no sending a scientist back to, say, research useful ways to get help), but the Lucian Alliance can somehow sneak past it. Word of God is that Atlantis had a fail-safe that required it be returned to the Pegasus Galaxy a few weeks later (this was to have been the plot of the Stargate Atlantis movie had it been greenlit), which addresses only some of these omissions.
    • Justified with the Aterro device, an Ancient superweapon that destroys Wraith ships when they jump to hyperspace, but also causes stargates to explode when dialed. While the Avenger Program from SG-1 could have crippled the gate network and allowed the device to work safely for brief periods to help end the war with the Wraith, by the time that the Atlantis team figured out what had happened, Todd had already hijacked the Daedalus and set a course to destroy the device.
  • In Farscape, Zhaan is capable of camouflaging herself like a chameleon, but only uses this ability in one episode ("Bone to be Wild", Season 1). She is a plant and this is one of the few times she is in a forest, but one would think it would be harder for her to camouflage herself against something as complex as foliage, compared to the relatively uniform interior of Moya.
    • D'Argo's super-long tongue and anesthetic saliva gets forgotten every fifth episode or so. His arms and legs are bound, while a sole villain gloats nearby without a helmet, whatever shall he do? The funniest is when John asks him to knock him out in "A Prefect Murder", and D'Argo pistol whips him. And it doesn't work. John asks him to hit him again harder.
  • Doctor Who, both Classic and New Series, did this a lot.
    • At the end of the first Christmas special of the new series, the vast alien starship that had been menacing the whole planet is utterly destroyed by a colossal laser fired from beneath London. This fantastic weapon devised by Torchwood London from captured alien technology for the defense of the kingdom from extraterrestrial perils is never again mentioned, despite London being menaced by aliens so frequently that its citizens get into the habit of evacuating over Christmas so as not to be there when the monsters turn up. However, the same technology (or, at least, similar special effects) seems to now be incorporated into the Valiant, as seen in "The Poison Sky" so even if the main weapon was destroyed, it's not all gone to waste. At least, until "The Stolen Earth", when the Valiant is overwhelmed and destroyed by the Daleks off-screen.
    • The TARDIS has had many features used over the decades that were completely forgotten soon afterwards; drifting back to its owner if separated from them in time ("Revenge of the Cybermen"), The Space-Time Visualiser ("The Space Museum" and "The Chase"), the Hostile Action Displacement System ("The Krotons"), among others. Considering that the TARDIS was a museum piece even before the Doctor stole it almost a millennium ago and is highly temperamental even at the bet of times, it's entirely probable that these things literally don't work anymore.
    • Companions sometimes call the Doctor out on this in relation to the TARDIS. But it's conveniently stolen, missing, or can't be used due to the danger of crossing their own timestreams, which is apparently very bad.
    • At the end of "Partners in Crime" the Doctor discards into a rubbish bin a sonic pen which opened a deadlock seal when used with his own screwdriver, one of the few locks his sonic screwdriver can't deal with.
    • A machine that creates candy-bar-shaped Food Pills appears once in the 1963 season and is never seen again.
    • The Chula, first mentioned in "The Empty Child", produced nanobots capable of healing any injury and even reviving the dead, and in enough numbers to work over whole planets worth of people. Why hasn't the Doctor simply gone to Chula and got some for himself? One possible justification is that the Chula are implied to be warriors, with Jack's ship and the pod containing the nanogenes being a stolen Chula Warship and ambulance for patching up their soldiers, respectively. Such a trip might not only be too dangerous, but the Chula might not want to share this technology with anyone.
    • On the same subject, the Doctor seems to forget regularly that the TARDIS let him go to the most advanced medical facilities of all the space-time where they can cure basically any disease. Would have been quite useful a fair number of times, like in "A Christmas Carol".
  • Ever since Disney took over the franchise, teams of Power Rangers have been getting single special abilities while untransformed. Except in Ninja Storm and Jungle Fury, where these powers were highly plot important, the Rangers would generally completely forget they had these powers for a dozen episodes at a time.
    • In the original series, this happened far more frequently, with MacGuffins being introduced regularly and never being mentioned again. The worst was the Sword of Power, summoned by a brainwashed Tommy as part of a ploy by Lord Zedd to steal it. After regaining his mind, Tommy goes to great lengths to get it back, taking on the Monster of the Week single-handedly. He retrieves it... and it's never seen again. For that matter, it wasn't clear why it was so desirable in the first place.
  • Claire's blood in Heroes. It can heal people. It works on anything, and nobody even mentions it in situations where it might be useful (for instance, on Nathan at the end of season 3). Her blood had previously restored her adoptive father to life. A shame he didn't mention this when her biological father needed it, and her grandmother was frantic to preserve him. Even stupider, her grandmother should have already known about it because of Adam.
  • Happened so often in Knight Rider that it became one of the jokes of the series. Aside from the common stunts, Bonnie/April would mention off-the-cuff that they'd added some cool new feature to KITT... which just happened to be exceedingly useful for that episode's problem. Then, it would never be heard about again despite the gadget being a solution to a later problem. Only a very few added features went on to be regularly featured without being implied to have always been there (which invoked the reverse of this trope, why hadn't they been using it?)
    • A few gadgets were explicitly mentioned as being failures and being removed in order to avoid this trope when they were a little too powerful, such as the laser and device that let KITT drive on water.
  • In an episode of the 1950s The Adventures of Superman, Superman learns from a swami (or somesuch) how to divide himself into two by using the power of his Super-will. It was only used once. Each is only half as powerful as the full Superman so it makes sense for him not to use it all the time; but it would have come in very handy during all of those "you never see Clark and Superman at the same time" bits.
    • Another episode has him develop the power to walk through walls without smashing through them by brute force and doing major property damage. Like the splitting power, gets forgotten from then on.
  • Wizards of Waverly Place
    • In the movie, a bad wish of Alex's ruins her parents marriage. Too bad they didn't learn a spell that allows them to reverse time to correct such mistakes, like they were taught during an episode of the series. This spell would have been very useful in the fight between Juliet and Mason to keep both characters from getting permanently transformed once Mason scratched Juliet.
    • The improv spell, which does anything as long as you can make up a rythme for it. Although, the wizards lessons pretty much disappear after that one. Presumably, all the spells afterward were the improv spell, with a few exceptions.
  • In one episode of Angel, Wesley uses a flamethrower against a bunch of mooks. Despite fire being deadly to most things, especially vampires, this is never seen again. It would have been particularly useful when Los Angeles was being swarmed with vampires and there were too many for them to attack one at a time.
  • In Eureka, the cryo sleep chamber that was used to put Fargo's grandfather in suspended animation could have been used many times to buy time during emergencies where people are mutating or dying of some horrible disease.
  • Supernatural
    • The Colt. Sam and Dean spend the first part of season 5 trying to recover it, only to discover that it doesn't work on Lucifer. They never use it again, despite how it would still work on lots of the other things they fight (read: monsters, demons and most angels, at least, if not the Four Horsemen and the Gods in Hammer of the Gods). They do use it when they travel back in time to kill a phoenix in season 6, though, so it's not completely forgotten.
    • In "Holy Terror", Sam is possessed by an angel, and Dean needs a way to get it out. Kevin comes up with a ritual that will temporarily give Sam control, allowing him to expel the angel. This doesn't work, but not due to any problem with the spell -The angel merely found out about it beforehand and sabotaged the ritual. One episode later, in "Road Trip", Dean and Castiel capture the angel, still in Sam's body, and need a way to expel him. The only idea they can come up with is a deal with Crowley, that he enters Sam's mind and explains the situation to him in exchange for his own freedom. Except, now that the angel can't interfere, there was nothing stopping the original -and much safer- plan from working. So you've got to wonder why they didn't just do that instead.
  • From Battlestar Galactica (Reimagined): In the middle of season 2, Roslin's cancer takes a turn for the worse, and she's saved at the last minute by the unborn Hera's blood. Now it's likely that Roslin is not the only one in the fleet with cancer (indeed, the season 4 episode "Faith" involves another character with terminal cancer). Yet no one even suggests the possibility of using Hera's blood to cure other cancer patients (or to try it on people with other kinds of terminal illnesses, for that matter). Even more ridiculous is when Roslin's cancer comes back in the season 3 finale, the question of using Hera's blood to cure her again is brought up only once (and ignored) by a reporter. Arguably, this is also an example of They Wasted a Perfectly Good Plot, since they could have done an episode about the ethics of regularly harvesting a baby's blood for medical purposes.
    • The Blackbird would be another example. Admittedly, they have to scrounge up a lot of supplies and spares to assemble it together but considering that Pegasus had Viper production facilities, it would not be impossible to construct additional stealth ships once the original was destroyed. It would have come in handy during New Caprica or the battle of The Hub.
  • The Big Bang Theory has a rare non-F&SF example: Sheldon can be persuaded to do some things he finds ridiculous or inexplicable by telling him that the thing is a "non-negotiable social convention". This has been used a grand total of once in the show's history.
  • Every once in awhile this will happen in Kamen Rider due to the Heisei Series being more toyetic. However, one of the most notorious early examples comes from Kamen Rider X. In Episode 2, Jin Keisuke uses a two-barrel blowdart gun that manages to make short work of GOD minions AND stop the Kid Of The Week from being lynched. In spite of it looking like the coolest thing ever, it is never seen again.
  • Once Upon a Time:
    • The Evil Queen in has the ability, at least in the Enchanted Forest, to pull a person's heart out yet leave them not only alive, but subject to her will. It's implied or explicitly stated that she's done this many times, yet she has to send Snow White into the woods with the Woodsman to get him to cut her heart out mundanely, rather than doing the job herself and turning her hated step-daughter into a slave and puppet ruler.
      • Turns out she can do this in every realm, along with magicial abilities that allow her to throw fireballs, force choke people, throw them around with telekinesis and turn herself incorporeal at will. She frequently forgets to use them. Same thing with Rumpelstiltskin who has similar abilities.
    • Emma has the self-proclaimed superpower of being able to tell if someone is lying, yet when she is questioning Greg Mendell about whether he saw Rumplestlitskin use magic, although she has every reason to need to know, she can't tell that he is lying through his teeth.
    • True Love's Kiss cures all curses, yet Snow White and Prince Charming occasionally go looking for curses that have befallen one or the other.
  • The spirit board from Charmed, which was used for all of three episodes before disappearing in season three until it finally resurfaced for one last use in season 8.
  • In Time Trax, in some episodes the fugitives, after the requisite dose of TXP, were sent back immediately after S.E.L.M.A. emitted a "transmission tone", but in others, the paralyzed fugitive's body had to be hidden until a personal ad was placed in a previously agreed newspaper, so TRAX could retrieve the fugitive. (That without taking into consideration the oft-repeated assertion that the changes in the past wouldn't affect the future because Darien Lambert and the fugitives were sent to a parallel timeline.)

    Toys 
  • The ability of various BIONICLE characters to form a Kaita or a Nui has been all but forgotten, and had only ever been used a handful of times early on in the series. This can be attributed to the set designers not coming up with combinations for the later sets, though a couple of already existing combinations still didn't get to be used, even when they would have come in really handy. There is no in-story explanation for this: the writer simply doesn't want to use them.
    • Another seemingly forgotten "power" is the ability for a character to rebuild itself (since they're Built with LEGO). Granted, this ability apparently requires the character to have an amount of secret knowledge, have pieces lying around and having strong enough muscles to support a new body, but still... the ability exists and has been used to make the characters stronger, but only on one occasion (because the toys said so).

    Video Games 
  • Ace Attorney
    • When Phoenix first meets Maya and finds out she's a spirit medium, he comes up with the obvious idea - why not just summon the victim and ask them who did it? Maya replies that she's just in training and can't do that. In the next two games, not only is Maya more experienced, but Phoenix also meets an even more talented medium, Pearl, yet he never thinks of that idea again. The one recorded time that was actually tried before, the answer the spirit gave turned out to be wrong, and the summoning was used to frame Maya for a murder.
      • This tactic was used by the police to find Gregory Edgeworth's killer and it ended up botched (becoming the infamous DL-6 Incident). This may also explain why Phoenix doesn't do it (may make people suspicious on the reliability and hurt his case). Also there's just not going there because it hits too close to home for Maya (whose mother was the unfortunate medium in said incident, something Phoenix didn't really gain a lot of appreciation for until the end of the first game).
    • Phoenix is in possession of what is effectively a magic lie detector. Given that Phoenix never chooses to defend guilty clients, you'd think he'd use it to help pick which cases to take. He did use it for this purpose once, but it misled him due to a contrived case of Exact Words, and he was forced to take said case either way. Still, you'd think it would be relatively reliable.
  • Freelancer, period. "Cloaking ships? What do you mean they were mounted on fighters during the Alliance/Coalition war centuries ago? They take more power than a battleship can provide! Besides, what war are you talking about? I've never heard of it before."
    • They also forgot the fighter-sized warp drives. They used 'em about the same time as the fighter-sized cloaking devices. Those Libertonians really ought to pack some Phlebotinum next time they go somewhere.
    • Neither of these examples really work in the context of Freelancer. Gameplay-related licenses with scale aside, Freelancer fighters are centuries more advanced than their Starlancer counterparts and can traverse solar systems quite easily on their own cruise engines. They can also use trade lanes, which are just as fast as warp gates were, while being much easier to utilize and maintain. Cloaks in Starlancer were also only really an ECM that made it impossible to maintain a sensor lock, whereas the cloaks deployed by the nomads are true invisibility to all forms of detection.
  • In The Elder Scrolls V: Skyrim many guards tell you "I used to be an adventurer like you, then I took an arrow in the Knee." but in a world of Magic healing spells and instant health potions you would not think such a minor injury would be so debilitating.
  • The Phase Transit Cannon from Wing Commander II is never mentioned again outside of a brief note in the manual for the Kilrathi Saga compilation mentioning that it was discontinued due to technical problems, and the flash-packs from Wing Commander IV isn't mentioned anywhere at all in later Wing Commander games, as if the tech has vanished.
  • World of Warcraft could be said to have this. When questing it is not uncommon to be given an incredibly powerful item to help with the quest, for example a crystal that can fire a beam to shrink down giants, making them much easier to fight, to never be used again.
  • Crops up in City of Heroes. Interestingly, your character is often the Forgotten Phlebotinum; for example, NPCs often caution you to "be careful, these guys are dangerous!", even after your character has defeated monsters, giant robots, and demigods.
  • One of the most notorious parts of Mega Man lore: what happens to the weapons he obtains from the Robot Masters? In every game, he receives several invaluable weapons and tools, but by the time Dr. Wily escapes from prison for what feels like the hundredth time, Mega Man has discarded them. Among other amazing weapons, you'd think he'd keep something like the Ice Slasher note , Atomic Fire note , Metal Blade note , or the Flash Stopper note  on hand for when Wily predictably reappears, but no. Especially groan-worthy when you realize that he sometimes has to obtain these weapons for the second, third, fourth, or (rarely) FIFTH time in later games (such as the arcade and Game Boy titles).
    • Also extends to other games in the franchise, such as the X series. Here, it's even worse as Mega Man X loses entire suits of his own powerful upgraded armor. There have been exceptions, however..
    • Surprisingly averted in Mega Man Legends, where the Bag of Spilling causing Mega Man to lose all his good gear from the first game is justified at the beginning of the second game: Roll had to sell off all his gear to afford to repair their ship back to top condition.

    Webcomics 
  • invoked in The Princess Planet, Christi has a magic wand that can do anything, but has only ever used it twice because she prefers the challenge of outwitting her opponents.
  • Early in The Order of the Stick, when going to face Xykon for the first time, Durkon enchants Roy's sword with a disruptor spell, which would have destroyed Xykon completely with one shot if Roy managed to land a hit. That spell would probably have come in handy the next time Xykon showed up, but nobody even thought to mention it.
    • The Giant, the author of said webcomic, specifically said that he prefers to do things that way. Taken directly from his FAQ, "Q: In Strip #X, why didn't character Y take action Z? If they had done so, they could have avoided a whole lot of trouble. A: You just answered your own question. The strip is about the trouble these characters get in; if a tactic would result in an effortless solution to their latest problem, there would be little point in showing it, see?"
  • In Sluggy Freelance, an early Story Arc had Riff and Dr. Schlock work together to build a time machine. After the machine is destroyed by a potato chip (it was balloon based), neither of them ever tries building one again, despite Time Travel having more Deus ex Machina potential than anything else. Though considering how much trouble they get into dealing with Alternate Dimensions and how big a mess they caused with the last time-travel jaunt, even Riff would hesitate to use it.
  • A particular device in Special School is designed to make people (except certain psychics) to forget all about it.

    Web Original 
  • As pointed out in Yu-Gi-Oh!: The Abridged Movie, Kaiba never used the cards given to him by Pegasus ever again, even in episodes set later, and though they are able to defeat the Egyptian God Cards. Nor does anyone in the series ever mention either the Pyramid of Light or the Blue-Eyes Shining Dragon. Ever. (Granted, the movie wasn't part of the original storyline, neither anime or manga.)
  • In the first episode of Chad Vader, he is shown to have the ability to force choke people, and he uses it on a guy who annoys him. In later episodes, his nemesis repeatedly humiliates him, and he just fumes impotently.
  • Phaeton has Trayen, who often gets caught up in battle and forgets just what he's really capable of. And Teliha isn't very good at remembering her spells either.
  • Chuck Sonnenburg of SF Debris loves to call out Star Trek for forgetting that the ship has shuttlecraft, and was stunned when Firefly didn't (from his review of "Out of Gas").
    Chuck: They cancel this, and let Enterprise run for four seasons?

    Western Animation 
  • Events surrounding the second season finale of Avatar: The Last Airbender left many wondering why Katara, who had theorized that her vial of water from the sacred oasis retained healing properties, didn't make so much as an attempt to whip it out and use on the mortally wounded Tragic Hero Jet a few episodes beforehand. The DVD commentary has them admit that they forgot it, but said it wouldn't have worked anyway.
  • Transformers
    • Waspinator's Eye Beams that he shoots at Cheetor with in the Beast Wars pilot. He never uses them again in combat, even in the Season 2 opener, when Cheetor knocks his gun out of his hand and those Eye Beams would have been a nice alternative to running away. He did use them at one other time, when he and Terrorsaur (who was also using Eye Beams) were trying to cut into Tigatron's stasis pod, but as a general rule if a character on the show had that ability and wasn't named Dinobot, they only got used on very rare occasions, and got overlooked numerous times that they could have been helpful.
    • Transformers Generation 1 had both sides constantly creating weapons that would be a Game Breaker in the hands of non-idiots. Instead of being used for what they could be, they'd be used to create/stop the problem of the day, and then never be seen or heard from again. Also, the many, many, many one-shot powers displayed by individual Autobots that would never be used again. (Most iconically, the Pure Energy flail and axe used by Megs and Prime, respectively, in the series premiere only and never again.) They also suffered from No Plans, No Prototype, No Backup: If the ultimate weapon whipped up in the days since the previous episode gets smashed at the end, just making another is apparently never an option.
  • Xiaolin Showdown
    • The Shard of Lightning can freeze time, and Jack used it to steal most of the monks' Shen Gong Wu, and cause various havoc. The monks won it by the end of the episode. They could have used it to freeze time and just kill Jack, Chase, Wuya and Hannibal all at once.
    • The Golden Tiger Claws, which allow a person to create a portal to any location. It's introduced and done away with in Season 1, but returned to the heroes in Season 2. Despite that Dojo can sense the location of any newly active Wu, the heroes never decide to have Dojo use the Claws to warp there, instead of flying there slowly enough to let the villains reach the Wu.
    • The Reversing Mirror, which is restored at the end of the episode "Citadel of Doom", could easily be used to restore Wuya to her full powers and body throughout all of season 2. Jack had no interest in restoring her, and later in season 2 Wuya went to Chase Young's side, who also didn't use the Shen Gong Wu to restore her until he put his Evil Plan into motion simply because he doesn't give a crap about the Shen Gong Wu. And she can't do it herself, for obvious reasons.
    • The Emperor Scorpion, a Shen Gong Wu that can control any other Shen Gong Wu. After being used to defeat four Mala Mala Jongs (giant demons made of Shen Gong Wu) at once, it is sealed away in the vault. Neither the monks, nor the villains (who raid the vault every six episodes or so) ever take or use this supreme Shen Gong Wu ever again, presumably because it would make the show very boring.
    • In "The Black Vipers", Jack is seen flying away after being deceived into losing a bag full of Shen Gong Wu. You can see the Glove of Jisaku on his hand as he flies away. The Glove of Jisaku has the power to attract other objects - even other Shen Gong Wu. He even used it to steal a bunch of Wu at once in an earlier episode. Yet he doesn't use it here.
  • In the Dungeons & Dragons episode "Beauty and the Bogbeast", a magical river was introduced. At a particular time every year, it could take the heroes anywhere they wanted to go - Earth included. Naturally, they are forced to turn around, at the last minute, due to extenuating circumstances. They never seem to consider that there's nothing stopping them from coming back (it's not clear how long the series takes place over, but it can't be that much less) next year and making sure no one gets turned into a bogbeast this time. Even considering the source, if there was ever an episode to throw on the Fanon Dis Continuity pile anyway...
  • In Ben 10, Ben's Evil Counterpart Kevin 11's original power was the ability to absorb energy, useful for shorting out/controlling machinery and creating instant lightning blasts. As a side effect, he was also able to use it to absorb alien superpowers via physical contact. After using his ability to steal Ben's 10 superpowers, however, Kevin seems to completely forget about his original ability, even though he names himself "Kevin 11" specifically because he has 1 more power than Ben. He fails to use energy control in situations it would have been extremely helpful (i.e. when being held captive by robots), and also fails to absorb any more alien superpowers despite apparently spending a few months roaming the galaxy doing nothing except beating random aliens up. The alternate future episode "Ken 10" shows how useful this would have been, as Future Kevin finally uses his power-stealing ability to become a formidable combination of Sylar and Naraku.
    • In the sequel, Ben 10: Alien Force, Kevin's powers are even more limited, as he can only absorb the properties of solid matter. This limits his options in combat into turning into something tough like metal or stone, then running around punching stuff. However, absorbing the properties of energy makes him go insane, which usually makes it a bad idea.
    • Also in Alien Force, the DNAliens are all infected humans, but Ben finds out the Omnitrix is capable of curing the people and is able to help Gwen's brother this way. He then proceeds to forget that he can do this until the Season Finale.
    • Incredibly, Ultimate Alien appears to have forgotten about the Ultimate forms, which give the new show its title in one of its first episodes.
  • The Fairly OddParents. Sometimes Timmy Turner wishes for superpowers. Sometimes he doesn't unwish them. These actually show up later and affect the plot. Same with magical items, handwaved by saying that they were neglected or that Cosmo was screwing with them.
  • Space Ghost Coast to Coast. The episode "Snatch" has a segment that is pseudo-satirical of this trope. Although the device in that case is a mind erasing device, so at least it is feasible that the device is never remembered.
  • An episode of Winx Club has a double dip of this: A segment of a season 3 episode opens with Icy boasting about a new fire power Valtor gave her. In the Trix's battles against the Winx, including the one just a few minutes later, she doesn't use it (and in fact, it's Darcy who sets a library on fire in a later episode, not Icy). And during the battle in the same episode, Layla sneaks up behind Darcy and Stormy to tie them up, even though way back in the second ever episode, she sensed Bloom's presence behind a garbage can, even though Bloom was well out of her view. (However, the non-4K version does mitigate the stupidity in both cases somewhat.)
    • A season 1 episode saw Icy destroy Red Fountain by freezing it with a nifty ice dragon. Season finale, Icy doesn't even make any effort to use it to freeze Alfea, or to take on Bloom, who has an fire-energy dragon of her own.
    • Bloom was shown to be able to use her powers to revive the dead. It's not explained why Nabu is still dead. This was changed to breaking a sleeping spell in the 4kids version, which removes the contention entirely.
    • In early season 3 there's nothing stopping a blind Layla from waiting to use Queen Ligea's healing staff the next sunset after she uses it on its owner.
    • The Charmix from season 2. Sure, it was So Last Season, but there's nothing else preventing the fairies who hadn't earned their Enchantix from using it in season 3, especially like when they're battling the Trix. Yet the only time it's even mentioned in season 3 is when the school headmistress talks about Enchantix.
    • In the 21st episode of the third season, Nabu claimed that the reason he had stowed away on the Specialists ship was so he could practice his invisibility spells against monsters living in the area the Winx were travelling to. Nabu's ability to turn invisible hasn't been seen again since this episode. (Although it's possible that he used this ability off-screen during season 4's episode 20 when he went to the nature fairy Diana's castle to try to save the Specialists, but this is just a theory...)
  • Lampshaded/Parodied in Stroker and Hoop with Hoop learning ninja skills for plot-related reasons in one episode, but never using them again. It's then brought up in another episode. Turns out you have to actually continue practicing to maintain ninja skills. Who knew?
  • In Futurama, Richard Nixon's head uses a robot body in one episode, and Beck's head controls a small set of robot arms in another. If heads in jars can control robot bodies, why don't most of them do it?
    • The day Nixon was elected, he got himself a gargantuan robot body complete with integrated rocket launchers. Where did it go?
  • Birdman. The title hero can only recharge his solar powers in sunlight. This means that in almost every episode (exceptions: "The Menace of Dr. Millenium", "The Deadly Duplicator" and "Versus the Speed Demon") he runs out of power, is captured by the villain and he has to re-expose himself to the sun's rays to regain his powers. In episode 20 "The Wings of Fear" he develops "Solar Energy Storage Bands", which provide him with solar energy to replenish his powers when he's out of the sunlight. After this episode they're never mentioned again, even though they would have been incredibly useful.
  • Challenge of the Super Friends is notorious for this trope.
    • Lex Luthor invents teleporters, time machines, cloaking devices, a gizmo that sucks the Green Lantern Ring off its wearer's finger, etc., etc. ... uses them once ... and then then never uses them again, even in situations where one of them would save the Legion of Doom's bacon.
    • One particularly damning example has Luthor forget a piece of Phlebotinum only moments after acquiring it. When he time travels to alter several of the Super Friends' origins, Luthor switches places with Hal Jordan and becomes the recipient of Abin Sur's Green Lantern ring. He dons his own Green Lantern suit and uses the ring to fly back to the Hall of Doom, and then promptly puts his purple jump suit back on and makes no other attempt to use the ring. This after having been defeated by Green Lantern's power too many times to count!
  • Teenage Mutant Ninja Turtles (2003): In the Fast Forward season, the Turtles and Splinter are stranded a hundred years in the future with no way of returning to their own time... not one mention is made of their time-traveling friend Renet, who is supposed to keep an eye on the time stream and would almost certainly have noticed if the Turtles were suddenly in a different time period than they were supposed to. Then again, it could be the Turtles and Splinter were supposed to spend some time in the future.
  • My Little Pony: Friendship Is Magic
    • Season 1 is full of this. The Elements of Harmony (and Princess Luna) are completely forgotten about after the second episode, Twilight Sparkle never teleported after episode four, Pinkie's "Pinkie Sense" is never mentioned again, and while the Sonic Rainboom pops up later it is only in a series of flashbacks. Season two turned all of these and more into Chekhovs Boomerangs... for, in most cases, exactly one episode each, after which they all went back to being forgotten if Rule of Drama requires it. By the end of season 2 the teleport spell was casual use. Some of these were due to an instruction from Hasbro to avoid Continuity Lockout, since they wanted to be able to broadcast and syndicate the episodes in any order. That doesn't explain late-Season-1-Twilight's aversion to teleportation, though.
  • A Season three episode of The Simpsons saw Homer's half-brother Herbert invent a device that translated baby-talk into intelligible english phrases. During the episode, this actually allows Maggie to stop being the voiceless and actually interact with the rest of the cast. The device is never mentioned again, which is surprising from a show that frequently lampshades its own reliance on Status Quo Is God.


Forgot I Couldn't SwimContrived Stupidity TropesForgot to Feed the Monster
Forgot I Couldn't SwimStupidity TropesForgot to Feed the Monster
Fountain of YouthApplied PhlebotinumForgotten Superweapon
Forgot He Was a RobotSpeculative Fiction TropesFree-Love Future

alternative title(s): Forgot About The Phlebotinum
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