Useless Item

The programmers or writers come up with an element for the hero to use. It's all cool, but they forget to make (or Dummied Out) any enemies that are affected by that element in any way. Or they put an item in that cures a specific one of the Standard Status Effects, but the said status is AWOL.

Compare/contrast Useless Useful Spell, Lethal Joke Item, and Elemental Rock-Paper-Scissors. See also Antidote Effect, where it's strategic concerns that make something useless rather than programming ones, and Vendor Trash, where an item got no purpose at all other than to be sold away and maybe provide a little variation in eye candy.

Not the opposite of Use Item (arf arf).

Tabletop Games

 * In Magic: The Gathering's Commander format, which requires decks be exactly 100 cards, the card "Battle of Wits", which makes you win the game if you have 200 or more cards in your deck, is entirely useless. Two combos exists that could theoretically allow it to be used but 1: They are dependent an agreement with the other players, either how many sideboard cards you can have or on how cards that pull cards from outside the game are handled 2: Either combo can win the game several steps before Battle of Wits if you just attack normally with the infinite monsters you spawned.
 * Normally, sideboards are not allowed in Commander (also ante effects are banned (being not Vintage legal), so these things together mean you can't ever have more than 100 cards in your library). If sideboards are allowed, they are normally limited to ten cards (which is still not enough for Battle of Wits).
 * The card "Great Wall" blocks creatures with the Plainswalk ability. At the time of its release one card, Righteous Avengers (printed in the same set), existed with that ability and that card was terrible. Even after its release, the ability was only printed on a single digit number of cards and the only remotely decent non-parody one it appeared on was part of an extremely rare set only released in Asia, Australia and New Zealand.
 * A handful of cards are banned in every format due to legal reasons (gambling, requiring physical actions) and being horrifically tedious (Shahrazad). While literally unplayable, these will never reprinted and are valuable for that alone.
 * Deliberate/parody example: The official Girl Genius card game includes a Vampire Hunter card that affects only Vampire cards. There are no Vampire cards, just as the series itself contains a vampire hunter, but no vampires.
 * Though there are no vampires, there is a card that, by the rules (explicitly: it is used as an example of the card game's literal text-based mechanism for determining to what cards the "Instructions" on a given card apply) counts as one: the Vampire Hunter card.
 * Back in the day, the Yu-Gi-Oh! card game had a bunch of cards that were only useful against one specific card. Not a specific type of card, not a specific group of named cards, but a single, solitary card. 10 years later, most of the cards they were useful against have been banned, leaving them with no use whatsoever (except if they're monsters, in which case they might as well be effectless). Even before then, the cards in question were limited to 1, so there wasn't much chance of being used in fans' eyes, anyway.
 * At release Blue-Eyes Shining Dragon (then a western exclusive) couldn't be used because it required Blue-Eyes Ultimate Dragon, which had not been released in English yet.
 * Red-Eyes Black Metal Dragon requires you tribute a Red-Eyes Black Dragon with Metalmorph equipped to summon, but is worse in every way than than Red-Eyes Black Dragon with Metalmorph.
 * One set released a set of "Effigy" monsters, one for each attribute, that let them be treated as two monsters when tributing them to summon a normal monster of the same attribute. These were OK cards, except for Wind Effigy because they never actually printed a WIND normal monster that required two tributes. To this day the only legal monster Wind Effigy can actually be used with is "Simorgh, Bird of Ancestry", which was released the very next and randomly (as though it were added in response to the issues of Wind Effigy) has a clause that treats it as a normal monster when in your hand.
 * Return Zombie requires you have no cards in your hand during your Standby Phase to activate its effects. The effect would be great, except for the small problem that the Standby Phase is directly after the draw phase so barring being forced to skip your draw phase, convoluted combos, or the opponent using banned cards, you'll always have at least one card in your hand during the Standby Phase.
 * Elemental HERO Neo Bubbleman requires you have an Elemental HERO Bubbleman and Metamorphosis to summon. Metamorphosis is banned and will likely never be unbanned. Even if it weren't banned, using Metamorphosis normally on Elemental HERO Bubbleman would produce a stronger monster in any case.
 * Guardian Elma requires using Butterfly Dagger Elma, a card notorious and banned for its many infinite loops.

Video Games

 * In Lufia II, the "Sea Ring" is strong against "Sea Creatures", but the programmers didn't flag any monsters as "Sea Creatures".
 * Again in the same game, there is a Capsule monster with "Soil" attacks. There are no monsters with the "Soil" flag set.
 * The "Ghost" and "Dragon" Pokémon types during Pokémon Red and Blue. Subsequent generations have made much progress in balancing out elemental types and attacks.
 * "Ghost" type Pokémon were supposedly strong against Psychic types, but out of three Ghost type moves available in the first generation, one was a status attack, another only inflicted fixed damage, and the third was completely ineffective against Psychics due to a glitch in the Elemental Rock-Paper-Scissors chart. Worse, the only Ghost-type pokémon in the first generation were also part Poison, making them vulnerable to Psychic attacks themselves. Finally, the strongest first-generation pokémon (Mewtwo) was also a Psychic, making the Psychic elemental type an overall Game Breaker.
 * The other type that psychic Pokémon were supposedly weak against, the Bug type, consisted primarily of status attacks, and most of the Pokémon who learned any effective Bug-type attacks were partly Poison themselves.
 * Bug types in general were pretty weak in that game.
 * "Dragon" type Pokémon were supposedly strong against other Dragons, but the sole "Dragon" type move in the first generation inflicted fixed damage, ignoring elemental type bonuses and making it almost useless against the sole Dragon-themed trainer in the game.
 * Infamously, the Anti-MUTE spell in the original Final Fantasy is completely useless since there are no enemies in the game that can inflict MUTE status on your party.
 * Moreover the original NES version suffered from numerous internal bugs that included rendering certain spells (LOCK and XFER, for example) absolutely useless, and ignoring attack bonuses for weapons that were intended to be elemental or monster-specific (Giant Sword vs. giants, Were Sword vs. werebeasts, etc.).
 * Final Fantasy XIII is horrible for this. The game practically throws debuff protection at you, but the only debuff that shows up with any regularity is the near-harmless poison. That each accessory only guards against one debuff and starts with a 30% protection rate only makes it worse.
 * Keeping your leader guarded against Death for the last part is the exception.
 * Kingdom of Loathing has boots that offer "slight cute resistance". There's nothing that deals "cute" damage in the game yet, and, since the "cute" element is discovered during a Fifth Element parody set in the far future, there probably never will be.
 * In the early stages of Ragnarok Online, functions existed to cause or deter status damages like poison. The catch was that these statuses did not yet exist in the game.
 * In World of Warcraft, there is a troll vendor in Shattrath City who sells you various trinkets that are supposedly good at repelling certain mobs, none of which exist.
 * Griftah actually sells a whole variety of items, most of which do exactly what they claim to, but are nonetheless completely useless. However, one item he sells that has no use listed in its tooltip is a part you'll need to build a really cool device.
 * Castlevania: Symphony of the Night has plenty of weapons with obscure bonuses, one of which [the Were-Bane] gives bonuses against Were-Beasts. Unfortunately there's only one Were creature in the game (the Werewolf) and although a mini-boss originally, by the time you get this weapon is encountered as just as a random grunt in one specific area and is not much of a challenge as you're now a much higher level, and there's plenty of weapons with much higher base damage that eclipse the bonus you'd get anyway. On top of this, though, the sword is glitched, in that it does absolutely zero extra damage to them anyway! Mind you, the sword isn't /completely/ useless, as it's QCF+Attack move is a flurry of thrusts in the same vein as the Rapier's, and Were-Bane is stronger than the Rapier. It makes for a good off-hand weapon if you decide to forgo two-handed weapons and shields.
 * Fable (the 1996 point and click adventure, not the newer action RPG series) was absolutely chock full of items that are never used. Whether their uses were Dummied Out or they were never intended to be used and served only as red herrings is unknown.
 * Legend of Dragoon features three useless key items that serve no purpose other than 100% Completion- the War Bulletin, Lavitz's Portrait, and Kate's Bouquet.
 * In Secret of Evermore, the Magic Gourd literally has no effect on anything. Even the programmers couldn't remember what it was supposed to do.
 * Cosmic Fantasy 2 notoriously is a partly unfinished game which does not contain status ailments, but it has a full selection of remedies and accessories that cure and prevent such remedies, which are all are a waste of inventory space.
 * In the original SNES version of Final Fantasy VI, the 'goggles' item prevented the 'blind' status effect, which did exist, and there were enemies that used it, but due to a glitch the effect did nothing to you at all. The only thing the being blinded effect was it prevented Strago from learning lores cast in battle. One might say The Goggles Do Nothing.
 * In the SNES North American release of Final Fantasy IV, Fire Bombs. Originally seen in the opening, when Cecil uses one to dispose of enemies in a cutscene, most enemies that would drop them had them removed from the drop list. The one exception were Red Dragons. However, they only exist in the final dungeon, and all of the characters can greatly outstrip them in damage. Averted in other releases, where they appear earlier in the game, when they're much more useful.
 * In Dungeons and Dragons Online, random loot can generate a lot of items of... questionable usefulness, like race restricted Warforged (Living constructs with no need to breathe, and as such having Super Not-Drowning Skills) restricted item of underwater action (giving you Super Not-Drowning Skills, redundant with a warforged racial ability)
 * Jet Force Gemini has the fish food, which can be used to feed fish in ponds. There is absolutely no benefit to doing this.
 * Gunstruction includes Magpul Glock compatible magazines as an option for 9MM AR15 builds. As of version 4.5 however, it does not include any lower receivers capable of accepting Glock magazines, making it impossible to use Glock type magazines on a build. It also includes a flash hider threaded to mount a Vortex DC suppressor, but the Vortex DC is not yet included.
 * Knights of the Old Republic II has a few as remnants of the game being unfinished.
 * A few items grant Force Resistance, an additional defense that will sometimes prevent low level force powers from working on the character. Unfortunately, due to how the game's item spawning and level scaling systems work, and the low value of Force Resistance granted all enemy force users will have a high enough level to automatically succeed on their bypass check by the time an item can be obtained. Thus the only way these items will work for the player is if they're cheated into the inventory earlier than normally possible.
 * The feat Weapon Finesse (Melee Weapons) lets a character who acquires it use their dexterity instead of their strength to determine accuracy with melee weapons, including lightsabers. Right next to it in the menu is Weapon Finesse (Lightsabers), which costs the same resources to obtain and does the exact same thing but only for lightsabers. This is fixed in the fan-made but officially endorsed restored content patch, which grants Weapon Finesse (Lightsabers) for free as a reward for completing a restored training session side-quest.