Depleted Phlebotinum Shells

""Perfect job for these babies. Made 'em myself. Holy water, clover leaf, silver shavings, white oak... the works.""

- Hellboy

""First rule of business- turn every weakness into a strength.""

- Lex Luthor, Justice League

Our weapons are useless! The enemy is Immune to Bullets! What can we mere humans do against the unending procession of impervious foes?

Quite a lot, apparently. By making modifications to our puny earth weapons (or, more commonly, to the ammunition) the world can be saved without having to Nuke Em (which usually doesn't work anyway since 'nukes are bad').

Said modification usually include using the target's Weaksauce Weakness in the weapon, such as silver melted from crosses, UV ammunition, and Cold Iron. Expect the boss monster to be immune thanks to their Cross Melting Aura.

A sub-trope, or rather a particular use, of Applied Phlebotinum. See also Abnormal Ammo, Armor Piercing Attack, Kill It With Fire and Kill It With Ice.

Name based on depleted uranium ammunition used by various nations since the 1970s.

Garlic
Hard to work with, but great against vampires. There's even a certain basis in reality for this - garlic contains Allicin, a potent anti-biotic and anti-fungal agent. Remember that the original vampire myths described them as plague carriers instead of angsty nobility or teenage estrogen bait.

Comic Books

 * Batman: soaks his Batarangs in crushed garlic for dealing with vampires.
 * Blade: Blade's opponents are sent into anaphylactic shock by garlic based pepper spray.

Film

 * Hellboy: Hellboy adds it to his rounds just to be complete.
 * Played with against non-supernatural opponents in the Roger Corman film The St. Valentine's Day Massacre: a croaky-voiced gangster (played by a young Jack Nicholson) notes the belief that the garlic he's rubbed his bullets with will poison the wounds-- kind of strange given what's known now about garlic...

Literature

 * The Dresden Files: Try this for a cheap, effective vampire-slaying tool -- paintballs filled with garlic and holy water!

Live-Action TV

 * Ultraviolet: Instead of putting it in bullets, they put it in smoke canisters. Minimal effect on troopies, knocks the "leeches" flat on their backs.
 * Forever Knight: In the episode "Hunted", a hunter shoots Nick with bullets stuffed with garlic.

Video Games

 * Castlevania: The manual for the first game stated that Simon Belmont soaked his signature whip in garlic juice and holy water for seventeen weeks before assaulting Dracula's castle. This is kind of undone since one of the first powerups the game will give you after every respawn is a ball and chain weapon that replaces the whip, and retconned out almost entirely with the increasingly-complex history of the whip in later games.
 * Played with in Oblivion. One quest requires you to kill a vampire, and reading his diary indicates that he has a weakness to garlic. He's annoyed at the fact that he's the only vampire who possesses this weakness (so far as he knows), making him a walking cliche.

Holy Items
Weapons made from religious relics or containing pieces of such are often used against supernatural foes, often in combination with special materials.

Anime and Manga

 * Chrono Crusade: the Magdalene Order uses scripture-inscribed bullets laced with holy water as standard ammunition against demons. They also have a small number of bullets which use the power of one demon to blow up another, with near-nuclear effects.
 * The demon bullet was deemed a failure, however, another bullet called The Gospel is perhaps the most powerful anti-demon bullet around, which is described as "a magic bullet made of a rare kind of silver that's synthesized using alchemy which has a spell inscribed on it at an atomic level." The results are quite devastating.
 * Similarly, SOP for gun-wielding exorcists in Ga Rei Zero is the application of spirit water (sometimes via grenade) in addition to the aforementioned inscribed bullets. These elements extend beyond gunplay, notably with inscribed motorcycle wheels and a weaponized iron.
 * Hellsing: Alucard's bullets, like his gun(s), are made to order - each is made from the metal of a Lancaster cross that was specially melted down for the purpose. The fact that the rounds are also explosive-tipped helps as well.
 * He later receives a gun which fires Macedonium silver-jacketed bullets with blessed mercury (quicksilver) cores. Those don't need an explosive added, since mercury, being a liquid with about the same density as lead, virtually explodes upon terminal impact anyway.

Comic Books

 * Astro City: "Confession" story arc, a squad of alien invaders is armed with holographic crucifixes, restraining cables soaked in holy water, and a two-handed stake-launching revolver. They are thus armed because

Film

 * Hellboy: as mentioned in the opening quotation. In the comics, the shells also contain garlic and cold iron shavings, and in all depictions are fired from a gun crafted out of a church bell.
 * Dogma: Silent Bob kills the demon Azrael with a golf club he stole from a cardinal. As it turns out, the previous owner blessed it to improve his score.
 * Van Helsing: used a gas-powered fully-auto crossbow. It was only effective after dipping it in holy water.
 * Constantine: melts gold from crosses to make shotgun shells.

Folklore and Mythology

 * In Swedish folklore, lead bullets are not only "lucky", they are also the only way to hit various supernatural menaces like shapeshifters, witches and their familiars, and animals protected by fairies. But it can't just be any lead; it has to be taken from a church window, which makes the making of the bullets blasphemy.
 * As a sub-clause of good luck hunting bullets made from church window lead, writer Gunnar Brusewitz mentions a fish made from silver and hung in a church as a prayer for good catches for fishermen. However, it was stolen by a man who made a fishing lure out of it, hoping the supernatural power in it would give him fishing luck. When you (presumably) endanger your eternal soul to get bigger pikes, fishing is Serious Business...

Literature

 * The Dresden Files: The Knights of the Cross each carry one of three swords (a broadsword that may or may not be Excalibur, a katana, and a saber). Each sword has one of the nails used in Christ's crucifixion worked in the hilt. While Harry used to believe that the sword had little powers on their own, acting more as a symbol being powered by their wielder's faith, the swords have shown that they are more than mere pieces of steel.
 * It also provides us with an awesome vampire-slaying tool: a paintball gun loaded with garlic and holy water balls. It's up there with the stake machine-gun in Sluggy Freelance.
 * And then there's holy water balloons...
 * John Dies At the End: Dave and John use a Bible duct-taped to a baseball bat to fight supernatural monsters. Oh, and breath mints with the Lord's Prayer printed on them.
 * Felix Castor: Felix's landlord Pen fends off a succubus with a shotgun full of filed-down rosary beads. It seriously ruins the succubus's day.
 * In the Anita Blake books, in order to better kill vampires, Edward has been known to take a hollow point bullet, fill it with holy water and silver nitrate, and then seal it with wax.
 * George Macdonald Fraser's The Candlemas Road has an interesting inversion: a dying border reiver begs the narrator (a priest) to baptize his right hand. You see, his parents only baptized the rest of his body at birth: they wanted their son to strike "unblessed blows" (presumably in the hope that this would in some way damn his enemies to hell.)

Real Life

 * This one actually happened in the Middle Ages, with relics (bones and personal items from saints) being used in the ornamentation of swords and other weapons. They were intended to be "blessed" with special powers (notably less successful than in fiction).

Tabletop Games

 * Warhammer 40000: Many weapons for dealing with the daemons, who, while not Immune to Bullets, are damn hard to kill. The most obvious are the psycannon shells used by the Ordo Malleus. Depending on the source, these are either filled with various blessed materials or have anti-daemon runes and prayers carved onto them.
 * Combining with Kill It With Fire gives flamethrowers loaded with Holy Promethium (napalm with the mystical properties of Holy Water). The Grey Knights' Incinerator is the best known example.
 * The Imperium also has special psych-out grenades that negate the Psychic Powers of those who are hit. It is said they are made using a material that is created as waste by the life support system of the Golden Throne and emanates negative psychic energy. Yes, The Emperor's shit kills psykers. He's that Bad Ass.
 * The forces of Chaos sometimes make use of daemon shells, which are bullets or artillery shells with a daemon bound within them. One the shell hits the target, the daemon's energy is released, causing a very large explosion of warp energy.

Web Comics

 * The Adventures of Dr. McNinja: One quest featured...
 * Nunchucks made from Mother Teresa's bones,
 * These are, in fact nunchucks.
 * A Bo staff made from the largest known piece of The True Cross,
 * Sai made out of St. Peter's sword,
 * And bullets that had been in the Pope's mouth(wash).

Iron
Iron, often Cold Iron or meteoric iron, is a traditional ward and weapon against magic, especially The Fair Folk. The term "cold iron" comes down to us from folklore, apparently as a poetic form of words (much as "cold steel" was used in later times). In various fictions, the definition of cold iron varies greatly.

Comic Books

 * Elseworlds story Superboy's Legion: where Ferro Lad proves completely invulnerable to the Emerald Empress' magic.
 * In one Wolverine comic, the chestular protagonist is facing an opponent who is immune to any weapon forged by mortal man. He uses a weapon made of meteorite iron and forged by a demon to ruin said opponent's day.

Literature

 * Saga of Recluce: features two distinct types of magic: Order-mage and Chaos-mage. Chaos energy has difficulty working on iron due to the natural Order energy woven into it, making it a solid defense. Additionally, Chaos-mages tend to build up a large amount of the energy in their body, so direct contact with iron causes their skin to blister painfully, and in extreme cases can lead to death.
 * Redwall: Martin's ancestral sword is reforged by the badger lord of Salamandastron using meteoric steel in Mossflower. The same sword is used by nearly every protagonist and has always slain the Big Bad of each particular novel (though not always directly, sometimes it is just used to, say, cut a rope holding a giant bell directly above the Big Bad).
 * Discworld: any iron can be harmful to The Fair Folk (which makes Tiffany Aching's choice of a frying pan as a weapon an apt choice). However, some places are protected by a powerful magnetic field to keep any iron from entering. Nanny Ogg uses one of 's horseshoes, which can go anywhere (like ).
 * Considering an explanation, "cold iron" on Discworld is an overstatement and means just "below Curie point".
 * Born to Run: humans fighting The Fair Folk with, among other things, shotgun shells loaded with "Cold Iron, holy herbs, and blessed rock-salt." One character also has a seltzer bottle that's been filled with iron filings and given a "pagan blessing." When he sprays the blessed and iron-laced water directly into a banshee's mouth, its head melts.
 * Soldier Son trilogy: iron beats any kind of magic and mages are "allergic" to iron. At the beginning of the series, the protagonist's country Gernia has subdued most of the magic-using peoples around them by switching from lead to iron bullets.
 * Warlock In Spite Of Himself series: iron in any metallic form is potentially deadly to the Little People. A handful of nails thrown into the bushes by a villain in one book is answered with cries of pain. And hanging scrap iron around your house also prevents the Wee Folk from entering. (The first book's claim that "witchcraft" (Psychic Powers) can't affect iron is RetConned away very early on).
 * The Spiderwick Chronicles book four: Jared confronts a faerie by pulling out a steel knife. His reasoning was that faeries don't like iron, and steel is at least part iron. It worked.
 * The Dresden Files:
 * anything with a high-enough iron content is potentially lethal to faeries; Mab, Queen of Winter and one of the most powerful magical beings on earth, recoils from a steel nail in fright the second before it touches her skin. Harry explains in one book that iron is to faeries what nuclear waste is to humans -- horribly wracking, and to be avoided at all costs. He even takes down  with nothing more than.
 * Charity and her nail gun
 * As long as they have iron, ordinary bullets do extra damage against the fae as well - even if your opponent is the size of a semi.
 * The Bible: iron chariots are just better. Just ask the men of Judah, or, God himself. It means this trope is Older Than Feudalism.
 * The Name of the Wind: cold iron is known to be super effective vs "demons".
 * Steel Magic: modern day steel utensils (like forks) are effective against magical creatures.

Multiple

 * In at least some versions of the stories, vampires are slain with an iron pike rather than a wooden stake, and/or iron filings may be placed under a child's bed to ward off vampires.
 * In folklore, wood stakes and iron nails are used to pin the vampire in its coffin (and then other things can be done to the body). It then dies and decomposes (and isn't coming back).

Tabletop Games

 * Changeling: The Dreaming: Cold iron (defined as "wrought iron") does aggravated damage to changelings... and if they die by it, their fae soul never reincarnates. The explanation is that the discovery of Iron working (and the coming of the Iron Age) was responsible for the end of the Fae golden age on Earth. Changelings, being creatures of dream and symbol, are especially vulnerable to it as a result.
 * Later supplements explain steel not being so dangerous by the fact that it was invented by a powerful fairy long ago who sacrificed his life to insure it would be harmless.
 * In the successor game, Changeling: The Lost, "cold" iron (material that's 95% iron at least) pierces fae defenses and hand-wrought iron does aggravated damage to the True Fae. One of the explanations is that the True Fae made a deal with Iron to gain mystical benefits from it as long as they made sure no human hand could change its essence. Once humans discovered smelting, however, the deal was broken and Iron decided it wanted to do some interesting things to the kneecaps of the True Fae...
 * Hunter: The Vigil notes that the high-tech Hunter compacts and conspiracies, like The Cheiron Group and Task Force: VALKYRIE, occasionally use pure iron slugs in their guns when expecting fae activity.
 * Exalted: Fair Folk take extra damage from pure iron weapons (not steel or other alloys), and are resistant to non-iron. Woe betide the Exalt who's stocked up on magical artifacts with no iron weapons.
 * There's a hearthstone called "Cold Iron Bauble" that can be mounted in said artifacts, which makes them act like iron to Fair Folk.
 * And without that, a sufficiently strong Exalt is quite capable of defeating a Raksha in single combat.
 * And given that this is Exalted we're talking about, "sufficiently strong" means "a combat capable character at character generation". And a combat focused character would just wipe the floor with them.
 * Martially-inclined Raksha are a genuine threat to young Exalts--even warriors--of virtually any type, due to being able to have attributes and abilities at superhuman levels right off the bat, whereas Exalts are limited to the human maximum of 5 in either until they hit Essence 6 and (depending on the type of Exalt) may not have access to enough of the Charms that wrench the advantage back over to their side at character creation.
 * In Dungeons and Dragons, fae and Chaotic Evil demons usually have some measure of damage resistance that applies to all attacks, except for those made with cold iron weapons.

Video Games

 * Princess Maker 2: adventure section of the game, there is an NPC Elf that can change your daughter's statistics. However, he will run away if your daughter is equipped with iron weapon or armor. It's surprising how the developers thought of this, especially when the game came from Japan.

Web Comics

 * Tales of the Questor: has an interesting theory on "cold iron"; somebody mistranslated "north-pointing" as "cold", meaning "cold iron" is lodestone -- North Pointing Iron.

Web Original

 * Whateley Universe: "cold iron" is cold-forged iron or wrought iron, according to Word of God, even if some fans are still arguing about it.
 * The Salvation War: gives us iron-tipped artillery in the form of High-Explosive Anti-Demon rounds. Not that conventional (military-grade) firearms were any less effective against demons, over penetration of APFSDS rounds aside.

Western Animation

 * Gargoyles:Xanatos tends to cut out the middle-man and have most of his weapons made of iron composites, just in case. Oberon may be a Physical God but even he takes major damage from anything forged from iron. At one (slightly depowered to impress his wife) point he is brought to his knees by Elisa Maza ringing an iron bell. In later episode he's toying with the main cast but finally decides to fight for real when someone impales him on a home-made harpoon gun.

Kryptonite and other Green Rocks
If the enemy is an alien or monster with a very specific, non-mythological weakness, be it Kryptonite, Music, or Water.

Anime and Manga

 * Cowboy Bebop: once featured a Creepy Child that was really a boy that stopped aging and gained immortality from a weird cosmic event. A stone made during the incident was the only thing that could kill him and Jet and Spike carved it into a bullet to use it.
 * Tears to Tiara: has both the Holy Empire and use weapons made of Electrum, a holy metal, against Noble Demon protagonist Arawn. . In-game, any equipment made of Electrum given to non-human characters (elves, dragons, demons, etc.) is only as good as whatever they were wearing earlier. It doesn't lower their stats, but it doesn't boost them either.
 * One Piece: Devil's Fruit users are all weak to submersion in water (which is a pretty Weaksauce Weakness for pirates in largely oceanic world). Sea-Prism Stone is a rock that causes people touched by it to suffer the same power-nullifying and strength-draining effect as being submerged. Usually, it's used in handcuffs, restraints, and cages, but the marine Smoker walks around with a weapon made of the stuff despite being a Devil's Fruit user himself.
 * Justified in that he uses thick clothes to avoid contact with the thing in question.

Comic Books

 * Superman: Kryptonite is Superman's one true weakness (usually), so it's hardly surprising that it's been weaponized against him. The most spectacular being the occasionally mentioned K-Bomb, a Kryptonite tipped nuclear bomb.
 * At the beginning of Final Crisis, Darkseid kills with a time traveling Radion bullet -- Radion being the one thing that can kill any New God no matter how powerful. Near the end of Final Crisis,  shoots Darkseid with the same bullet which jump-starts the latter's Rasputinian Death.
 * In an interesting inversion, Bloodscream seems to be able to recover from attacks by Wolverine's adamantium claws. Guess what happens when he faces Wolverine without the adamantium.

Fanfic

 * Aeon Entelechy Evangelion: there are warheads enhanced with The Colour out of Space.

Film

 * X-Men: Origins: Stryker manages to bypass both Wolverine's adamantium bones and healing factor by shooting him in the head with adamantium bullets. The bullets pierce his skull, and while Logan's brain can heal, his memories can't.

Literature

 * Battlefield Earth: the Psychlos are very resistant to damage due to their inhuman physiology, but anything radioactive would react explosively to the 'breathe-gas' that they used for respiration. In this case, the humans defeat all the Psychlos by simply  Though really, an ounce of plutonium in a lead box would have worked equally well.

Live-Action TV
"Gen. Vidrine: You're telling me that a slammer missile could take out a Goa'uld mothership?
 * Stargate SG-1: The mission of the entire SG project was to exploit alien technology or hybridize it with conventional weaponry to defend the Earth.

Maj. Carter: When equipped with shield frequency modulators and naquadah-enhanced warheads... yes sir."


 * In the later seasons  prove to be functionally Immune to Bullets which necessitates research into some of these.

Tabletop Games

 * Rifts: The New German Republic has discovered that hot uranium rounds prevent supernatural beings from regenerating or even healing damage.

Video Games

 * Command and Conquer: both Nod and GDI use specialized munitions. In Nod's case, they have a love for filling missiles with various breeds of Tiberium-based explosives or gases, while GDI has developed sonic-based and EMP artillery shells and grenades.
 * Monkey Island series: root beer is an extremely effective ectocide. It only works on ghosts-- when Guybrush tries this on the resurrected Zombie Pirate LeChuck, he shakes it off and chastises Guybrush for trying to off a zombie with a mere soft drink.
 * Super Robot Wars OG Saga: Endless Frontier: Though not particularly used against live targets, Haken's Night Fowl requires special bullets to destroy the Mild Keil crystals causing Broken Bridge antics and other chaos in-game. To ensure they're strong enough for the job, they're made from (or based on the composition of) fragments of the crystal type they're made to break.
 * Hunter: The Vigil: Task Force: VALKYRIE uses bullets treated with the power of SCIENCE! to turn them into super-high-energy rounds that can strike and harm incorporeal targets like ghosts.

Web Comics

 * Nobody Scores: one of the characters acquires a hunk of Kryptonite and goes to sell it to Lex Luthor. Superman takes them out from long range with a traditional sniper rifle of his own before they even spot him.

Magic Imbued
When only magic can affect a monster, sometimes infusing magic into a more mundane weapon will do a better job.

Anime and Manga

 * Fate Zero: Emiya Kiritsugu's custom "Origin Bullets" were filled with his own powdered bones, which contains Kiritsugu's dual Origins (base 'orientations' of an individual) of 'Binding' and 'Severing'. A magus uses magecraft to defend against the bullet? The Origins are forced directly onto his Magic Circuits, overloading them and ripping them apart.
 * Mahou Sensei Negima: Tatsumiya creates her own spell-imbued bullets for exorcisms and the like..
 * Outlaw Star featured Caster shells. Although the exact terminology fluctuated slightly depending on who was doing the talking (and who was dubbing/subtitling the episode), it all boiled down to "big ass guns that fired bullets which exploded into magical spells." The guns themselves were rare, but the more simple Caster rounds were relatively easy to find; when Gene needed to get the really good ones to take on the Big Bad he needed to track down the trio of semi-ageless techno-sorcerers that made them in the first place.

Comic Books

 * Hellraiser: In the "Razing Hell" comic mini-series, written by the Wachowski Brothers, the protagonists manage to make bullets out of some of their own bones (starting with a fallen comrade who tells them how to do it with his dying breath, and later, in one desperate situation, a character uses his own pinky finger to make more ammo), since one of the only things that can hurt the Legions of Hell is Leviathan's own power (which has tainted them too, since they were its prisoners). They use this knowledge to begin a grim but very effective La Résistance campaign against the cenobites and the puzzle-box guardians.
 * Superman: in the Silver Age Kryptonians could only be harmed by three things: other Kryptonians, kryptonite, and magic. So if you don't have any green rocks handy, get that Billy Batson kid to shout Shazam near him.
 * To take down Black Adam, a bullet was made from a piece of the Rock of Eternity

Literature

 * A Song of Ice and Fire: The Others are creatures born of winter and hate everything warm. Though they fear fire, their speed and combat skill makes them difficult to set alight. Fortunately, in this world Valyrian steel and obsidian (also called dragonglass) are associated with dragon fire and can slay them. A flimsy obsidian dagger wielded by the obese and combat-aversive Samwell Tarly pierces an Others' ice of armor like butter and actually melts its hands when it tries to pull the knife out.
 * Tortall: griffin-fletched arrows always hit their targets, and Stormwing-fletched arrows go through magic shielding.
 * Night Watch: it's very difficult for an Other to be killed with human weapons, as their instinct is to jump into the magical dimension of the Gloom at the first sign of danger, where physical objects cannot reach. Only enchanted bullets have a real chance of killing an Other. A human working for an Other is given enchanted bullets for his submachinegun. These bullets end up killing a werewolf. Besides that, only a nuke can definitively kill an Other, because nuclear explosions somehow reach even the deepest levels of Gloom.
 * The Dresden Files: The enchanted silver swords the Wardens use can cut through enchantments and dispel physical attacks... as well as cut through nearly anything else (such as trees).
 * Special Circumstances: Generally speaking, weapons imbued with the spirit of a member of the titular organization are often either the only way or the best way of slaying a supernatural beastie. There's also a discussion, at one point, of how normal, non-spiritual FBI agents could battle the supernatural, using "Cold Iron" bayonets for their rifles.

Tabletop Games

 * GURPS Technomancer: The magical metal Necronium, is used primarily as a power source (and can sometimes poison those exposed to it and bring them back as the living dead), whilst depleted Necronium is toxic to all magical creatures. Depleted Necronium is also completely unaffected by magic, allowing it to penetrate nearly all protective spells.
 * Mage: The Ascension: Primium for the Technocracy, which is essentially a kills-supernaturals-dead weapon. Using it in a laser makes its wounds as agonizing to vampires as sunlight, Primium bullets hurt werewolves like silver does, and if you're afraid of magic users, plating yourself with Primium stops magic dead (some of the time at least.)
 * Mage: The Awakening: (the new World of Darkness' version of the above game) we are given Thaumium. It stores magical energy, it's resistant to magic, and it can cut through anything. Just for added punch, it's made from silver, gold, and mercury, all of which have to be mystically purified to produce the essential platonic essence of their being. Yes. Thaumium is made from a mixture of depleted precious metals.
 * Warhammer 40000: Thousand Sons chaos marines use inferno bolts, bolt rounds infused with chaos power which can pierce power armour with ease.
 * Dungeons and Dragons:anything under rules with DR x/Magic (Damage Resistance of x points negated by Magic) will have a certain number of damage points deducted from any incoming non-magical attack. In extreme cases, a Redshirt Army's worth of mundane arrows will be unable to harm a monster. On the other hand, one Player Character using a magical bow to negate the resistance can defeat the same monster using the same arrows.
 * Eternal Darkness: any weapon can be enhanced with magick. Imbued projectile weapons, including crossbows, rifles and shotguns, launch/fire imbued projectiles. It's not necessary to killing monsters, but sure helps.

Video Games

 * Fatal Frame/Project Zero: the character is often an otherwise ordinary person who has the misfortune to "see things other people can't see", which inevitably leads to trouble when they stumble into the haunted house/village/island populated by the restless spirits of the dead. The main weapon used to fight these incorporeal nightmares? A camera. Yes, a camera. One which uses some sort of special crystal or mirror in its makeup so that the user can see ghosts, dispell mystical barriers, and drive off the dead with the snap of a picture.
 * Eternal Darkness: you can cast an enchantment spell on your weapon that can boost damage. If you use the alignment rune (IE: using the Xelatoth rune on monsters aligned with Chatturga), it boosts damage even more. Some weapons are firearms, especially in some of the levels based closer to present-day. Wanna plug a minion of an Eldritch Abomination with a WWI-era Enfield rifle imbued with the power of that Abomination's rival?

Web Comics

 * Two Kinds: the most efficient way to take down one of the series Evil Towers of Ominousness is to shoot the tower's core with a magic-imbued arrow.

Silver
Silver weapons, including Silver Bullets, are commonly used on Werewolves and (less frequently) Vampires, stemming back to the idea of silver being a pure metal and/or associated with the moon. (Note that in Real Life, silver and copper do have biocidal properties. The idiomatic "silver spoon", as well as the common brass doorknob, is very effective at killing bacteria on contact. Silver nitrate is one of the oldest disinfectants, and one of the few such remedies still commonly used.)

Comic Books

 * Werewolf By Night: the armor and weaponry of Moon Knight was specifically tailored for werewolf fighting, laced with silver throughout.
 * Batman: story pits Batman against a vampire, whom he kills (he did that back in the day) by melting down some silver candlesticks, forging bullets out of them, and shooting the vampire.
 * Fiends Of The Eastern Front: the main character melts down silverware and forges them into bullets for his machine gun to fight Constanta's vampire troops.

Film

 * Underworld: the vampires fight with bullets filled with silver nitrate . Considering how thick and silvery it is, one assumes it is a VERY saturated solution (silver nitrate is usually thin and black).
 * Blade: at least the film and TV adaptations, uses silver-coated steel in his melee weapons (spikes and swords).

Literature

 * The Dresden Files: tightens the qualifications by having a cursed werewolf that can only be killed by inherited silver.
 * The Bartimaeus Trilogy: Silver is used as a weapon against spirits, since Silver actually causes damage to their essence, and can destroy them if given enough time. Iron also works to a lesser degree.

Live-Action TV

 * Blood Ties: Detective Mike Sellucci is given silver bullets made for his police-issue Glock 9mm to kill a wendigo. He pumps it full of silver before the creature explodes.
 * Friday the 13 th The Series: a werewolf was strangled with a Kodak film roll with silver in it.
 * In True Blood, the Fellowship of the Sun sent a suicide bomber whose bomb-vest was layered with silver shrapnel to attack a social gathering of vampires and friends.
 * In Supernatural, silver blades and bullets will dispatch zombies (reanimated by dark magic), shapeshifters, werewolves and more.

Tabletop Games

 * Werewolf: The Apocalypse: werewolves use silver knives on each other.
 * Werewolf: The Forsaken: if silver touches a werewolf's blood, it burns them for aggravated damage and has a rare chance of messing up their Healing Factor. Unlike in Apocalypse, however, using silver on another werewolf is a major sin on the Karma Meter. It's also implied that the Pure get messed up worse than the Forsaken because they never sought forgiveness from Luna for the death of Father Wolf.
 * Hunter: The Vigil: even the lower-tech groups, are known to use silver bullets in their guns, though they don't always use them against the right enemies (i.e. werewolves).
 * Dungeons and Dragons: there are rules for coating any weapon with "alchemical" silver. This applies a penalty to using the weapon so many players will carry a silver coated sidearm. Magical weapons typically don't need coating.

Web Original
"1117. Can't strangle a werewolf with a roll of Kodak film, no matter what we all know it's made out of."
 * Though some variants apparently are over the top:

Western Animation

 * The Curse of the Were-Rabbit: the bullets needed are gold. Twenty-four carat gold.
 * Parodied in a Robot Chicken sketch: A werewolf is shown running from some kind of hunter and gets shot. The werewolf then claims "Only a silver bullet can kill a werewolf!". The hunter then proceeds to shoot the werewolf into a bloody pulp with a chain gun, light the mess on fire, snort the ashes, crap it out on a toilet and get processed in a sewage plant. Cut to 3 kids playing some sort of tabletop game, with the game master reading from the book and saying: "It says it's STILL not dead!"

Video games

 * Blood Rayne: Agent Rayne has blades either coated with silver or made of a silver alloy.

Ultra Violet Light
A common way to kill vamps, using UV rounds, grenades, lamps, or other tricks. The implication is that a number of supernatural creatures are susceptible to ionizing radiation (by definition, light capable of tanning skin is ionizing), which is often used to sterilize tools and food, tying into the concept of supernatural creatures as plague carriers. It also means that someone should perhaps attempt to kill vampires with X-ray machines or plain 'ol depleted uranium.

Advertising

 * This Audi commercial.

Anime

 * Ergo Proxy: the only way to kill a Proxy is with shells that emit UV radiation, because the Proxies.
 * In Gantz Kei at one point uses a UV lamp to great effect against vampires.

Comic Books

 * Blade: has flashbangs and UV flashlights.
 * Paralleled on occasion in some weapons against Superman developed from the spectograph of Rao (Krypton's red sun) which takes away his powers until he is again exposed to solar rays.
 * Notoriously used by the Soviet Union in Frank Miller's classic, Batman: The Dark Knight Returns who had tempered a high-yield nuke to do as much ecological damage as possible. Effects included a hemisphere covering EMP and a dust cloud that blocked out the sun in very literal nuclear "winter" way. Since Superman was trying to intercept and redirect the ICBM, it almost kills him because he is left with almost no exposure to his solar power source (he somehow drains energy from some plants to get back on his feet, but is still noted to be operating well below his peak power weeks later).

Film

 * Van Helsing: had a full spectrum sunlight grenade. He didn't know what it could be used for, but he thought it would come in handy.
 * Underworld: As pictured above, the Lycans go armed with bullets filled with a liquid that emits ultraviolet radiation. It works very well.
 * Near Dark: Although unintentional, the cops' use of ordinary ammunition to punch holes in the walls of the room where the vampires hid, thus exposing them to criss-crossing beams of sunlight, at least brushes the boundaries of this trope.
 * The same thing happens at the end of From Dusk Till Dawn.
 * Nightlife: a hematologist creates a "prison cell" for a vampire by strategically positioning ultraviolet lamps.
 * Thirty Days of Night: ultraviolet causes severe burns to vampire. Unfortunately the protagonists couldn't (or just plain didn't) use it effectively
 * Blade: Has UV lights on his car and weapon-mounted tactical light. Hannibal King's guns shoot UV-radiating bullets.

Tabletop Games

 * Dark Conspiracy: had ultraviolet lasers for use against vampires.

Video Games

 * Vampire Rain: the protagonists fight the titular vampires with UV knives (which can only be used once) in addition to their arsenal of conventional firearms.

Web Comics

 * In Derelict UV crossbow bolts appear to be the protagonist's chosen weapon against her robed and masked enemies.

Wood
If the enemy, usually a vampire, is vulnerable to wood, the solution is to upgrade the stake into a wood tipped bullet or more powerful and faster reloading crossbow.

Comic Books

 * Blade:In his original comic book appearances, Blade used knives made from the hardest teak wood against Dracula and pals.

Folklore and Mythology

 * Norse Mythology: only mistletoe could harm Balder; everything else in the Nine Worlds had promised not to hurt him, because Balder was just so damn pretty. (The mistletoe probably would have promised too, but Frigga forgot to ask it.) Magnificent Bastard Loki simply could not resist the opportunity this presented...

Literature

 * Sherlock Holmes: wooden bullets were used to threaten the Count in The Holmes-Dracula File.

Live-Action TV

 * Buffy the Vampire Slayer and its Spin Off Angel: both use crossbows, and Angel has two devices that extend stakes hidden in his sleeves. Connor also used an automatic-staker in his first appearance as a teenager.
 * In True Blood, the Fellowship of the Sun developed quite an arsenal of wood-tipped projectile weapons.
 * Wood is used against vampires all over The Vampire Diaries, in forms ranging from a standard hand-driven stake to a crossbow to wooden bullets that can be fired from a standard pistol.

Tabletop Games

 * Rifts: has wood-firing railguns (with embedded metal cores for the magnets to work on) on occasion for dealing with vampires. It also has actual depleted uranium shells (Not quite depleted, as these were described as still being more radioactive than normal DU rounds), which for reasons unknown retard magical abilities to heal. These are great for those pesky critters that fight you down to their last MD point and then teleport off and return an hour later fully healed, giving you the time to hunt them down and finish the job. There are also shells made of non-depleted uranium that actively interfere with magic use by anything they embed in. Both can be cured by physically removing the round, however digging into your side with your own claws is generally A Bad Idea.

Video Games

 * Saga Frontier 2: Wooden swords are the weapon of choice for most people the world, since magic cannot be channeled through steel weapons. One character uses this limitation to his advantage, however.
 * Hunter: The Vigil Task Force: VALKYRIE sometimes uses specially treated wood bullets against vampires-the bullets can come in all sizes, and can be used to effectively "stake" a vampire at range.

Web Comics

 * Sluggy Freelance: Riff comes up with this baby. Too bad it only holds one second's worth of ammo and takes two days to reload.

Everything at Once
For weapons that combine various weaknesses into one shotgun shell, sword, or what have you. Just to cover all the bases.

Comic Books

 * Astro City "Confession" story arc (see above): Mordecai Chalk, a cyborg monster-hunter. He had a shotgun that fired shells with wolfsbane and holy water, mechanical parts etched with holy symbols and crafted in iron and silver, and an on-board computer that references thousands of occult tomes.

Fan Fiction

 * In When Titans Clash by Tenhawk, the Knighthood used counter-supernatural artillery rounds that were "... based around a core of three kilos of military grade high explosive which was surrounded by a sphere of blessed silver segmented into frangible pieces approximately one cubic inch in volume. This was in turn surrounded by pure meteoric iron in a second sphere, segmented into similar pieces."

Literature
""Like many barmen, Igor kept a club under the bar to deal with those little upsets that occurred around closing time... Igor's weapon of choice was a little different. It was tipped with silver (for werewolves), hung with garlic (for vampires) and wrapped around with a strip of blanket (for bogeymen). For everyone else the fact that it was two feet of solid bog-oak usually sufficed.""
 * Discworld: In the undead bar of Ankh-Morpork, the bartender, Igor, has a weapon as follows:


 * Star Trek the Next Generation: "Greater Than the Sum" introduced a "multivector weapon" designed to use everything against the Borg that had ever been somewhat effective. Then the Borg got ahold of it before it could be used against them--and did what they always do--they adapted.
 * The Bartimaeus Trilogy: All spirits from the weakest mite to the greatest marid can be severely hurt by silver, iron, and certain types of herbs and spices, such as rosemary. Magicians, commoners, and other spirits exploit this to no end. It gets to the point where powerful spirits are taken down by improvised use of everyday metals more often than they are by the devastatingly destructive spells these entities can employ.
 * Reserved For The Cat: the heroine carries a revolver loaded with two Cold Iron bullets, two Silver bullets, and two Blessed Lead bullets, plus extra ammo of all three types. It's anyone's guess which type offed the mystical Big Bad at the end of the novel.

Live-Action TV

 * Supernatural: the hunters have to improvise a variety of weapons to kill a variety of creatures. The hunter's arsenal makes use of most of the above, except garlic. The most frequent example is their use of shotgun shells loaded with rock salt against ghosts. Ghosts cannot act on iron, and are killed when their remains are salted and burned. Bobby's saferoom is walled with Iron treated with rock salt. Holy weapons can be found with holy water, which cannot be crossed by demons, or holy oil, which cannot be crossed by angels. This has even been weaponized into a molotov cocktail. Angels also can be killed by And when all else fails, there's a magical gun and knife that kill everything.

MMORPGs

 * City of Heroes: this may be the only explanation for heroes with assault rifles being able to take anything down at all. Unfortunately this works the other way, too, as mooks and bosses of a high enough level can worry heroes protected by magical forces, power armour, and the like with ordinary guns.

Tabletop Games

 * Dungeons and Dragons: includes a plethora of monsters with varying types of damage reduction, such as werecreatures, demons, fey and others, which often results in adventurers carrying around extensive collections of weapons ("No, we need a silver magical weapon that does piercing damage, not a cold iron one!"). Both melee weapons and ammunition for projectiles are often made from these special materials.
 * An insanely genius item introduced in one of the Van Richten's Guides was a weakness-detecting arrow. Rather than a traditional point, it had needles from over a dozen different substances, like cold iron, gold, silver, wood, and so on. When fired, it does minimal damage to its target, but also does not embed itself. After it is recovered, the wielder can see what substance did the harm based on which other needles are broken or bent, and (depending on the target) which needle has the blood stain.
 * This is parodied in Order of the Stick. When Haley is faced with Sabine (a fiend) she is unsure whether to use silver or cold iron arrows. She compromises by simply firing both at the same time.
 * Which causes damage but then she still doesn't know which arrow did the damage.
 * Epic-level monsters (i.e. challenges for level 21+ characters) sometimes require truly bizarre weapons to deal normal damage to them. A time-elemental Phane can only take normal damage from weapons from an alternate history, for example, and a mind-consuming Dream Larva only takes real damage from weapons forged by a sleepwalking blacksmith.
 * For this reason, a DM also needs to be careful when importing monsters from other settings. There's nothing more hilarious than releasing some monster from Eberron that only takes full damage from byeshk weapons into a world with no byeshk.
 * What of the creatures that can only be killed by reducing them to negative hit points, acid bath, burning, and multiple Wish spells? Damn Tarrasque...
 * The Regeneration Ability that stops a creature from being killed by attacks that do not overcome it. For example trolls can only be killed by fire or acid damage.
 * There are magical weapon enhancements that can compensate for the "golf bag scabbard" problem. Metalline weapons overcome any damage reduction based on the material composition of the weapon, Transforming weapons can change shape into other types of weapons which deal damage in a different manner (bludgeoning, piercing, slashing, or some combination), and Shadowstriking weapons can temporarily attune themselves to a particular creature and overcome whatever damage reduction it happens to have.

Video Games

 * The Elder Scrolls: many of the enemies are immune to typical weaponry. Spirits in particular can only be harmed by silver, daedric, or magical weaponry. Oddly enough, beating the bejeebus out of ghosts with your bare hands is more effective than some of the most powerful types of swords and axes in the game.

Web Comics

 * Parallel Dementia: Fall and other Nightmare hunters use blessed weapons (to combat demons), obsidian (for angels), garlic (for undead), iron (for fey), amethyst (for spawn), and silver (for therians) to combat the various types of Nightmares.
 * On at least one occasion, Fall is given specially made ammunition incorporating all of these at once, because she's about to head into an extremely tense situation and standard operating procedure (using a test clip loaded with one of each kind of ammo, in a specific order, so that you can switch to full clips of the appropriate variety when you find the one that works) would be dangerously time-consuming.

Web Original
"Silver bullet; hex-scored jacketed hollow-point filled with a gel made of Holy Water, wolfsbane, garlic, fugu toxin and curare, laced with dimethyl sulfoxide to provide tractor-solvent Spreading Factor. Traditionalists can also cut crosses in the bases of the bullets, and have them blessed by a priest. .44 magnum 240-grain load over the standard Elmer Keith hunting load, 24 grains of IMR 2400 (the manual says 21.8 grains is maximum, so don't use the 24-grain load if you have a cheap revolver). These work reliably on Vampires, Werewolves, the generic Undead, and Evil Human Minions like Renfield, with sublime indifference."
 * The legendary Usenet poster 'Gharlane of Eddore' once proposed a design for a Standard Generic Monster Load, which was:

Other
If bullets won't kill it, then obviously the answer is to make better bullets. If they're just really well protected, use a harder material like bronze or tungsten. If somebody's playing tricks with magnets, use compressed plastic. With magnesium, you can Kill It With Fire! Or perhaps you can recycle their phlebotinum and Hoist Them By Their Own Petard.

Anime and Manga

 * Elfen Lied: When traditional firearms prove useless against the diclonii, the antagonists resort to anti-tank rifles loaded with purpose-made tungsten slugs.
 * Kittan in Tengen Toppa Gurren Lagann at one point attempts to hold off a Mugann with a shotgun packing "Spiral shells". A more impressive one is issued to Grapearls, producing huge explosions and a shell to contain the aftermath of a Mugann going blooie.
 * Sven from Black Cat packs an array of interesting bullets, and among these there are blue-tipped ones that freezes the opponent on contact.

Comic Books

 * X-Men: Magneto, Master of Magnetism is often faced with plastic or composite weapons, and was locked in a "plastic prison" on more than one occasion.
 * In the original animated series a Sentinel boasts about how its plastic coating stops Magento's powers... Magneto's response is an annoyed "You fools, this whole ship is my weapon! and promptly throws the huge generators nearby through the Sentinels.
 * The Mighty: Gabriel Colewas given some special bullets. It turns out that it's
 * The Daximites, a race of aliens which has Superman's powers, only weakness is LEAD, which means that any attempt to take over the Earth while firearms and lead bullets are the most common weapondry on the planet is pretty futile.

Film

 * Transformers: The "6000-degree magnesium burn" of "high-heat 105mm sabot rounds" fired from an AC-130 gunship allowed the US military to hurt the marauding Decepticons in the movie (it's not much, but it worked rather better than normal bullets). Discarding-sabot rounds being neither hot, magnesium-laden or used by AC-130s, this has little to do with military practice or actual physics, though it is implied that weapons technology in the movie-verse is different because many human technological advancements came from studying Megatron's body.
 * By the second movie, the human NEST teams are shown carrying heavily-upgraded, large-caliber assault rifles and machineguns that can actually inflict damage on Decepticons; the NEST units and Marines fighting the Decepticons at the end of the movie prove surprisingly effective against the Decepticons in the all-out battle that results.
 * In Posse, Jesse Lee has some of the stolen gold recast into golden bullets he intends to use on his father's killers. Father Time explains that, according to New Orleans voodoo ladies, gold is the only way to kill a demon. In Jesse's case, the demons are symbolic rather than actual.

Literature

 * Hammerverse: there's all sorts of strange weapons and ammo. One example is the "osmium penetrator" used by some of the other merc companies. These weapons take a rod of osmium, put behind it roughly a liter of propellant, and force it down a diamond-coated barrel to flechette thickness. It emerges as a osmium needle well capable of getting through tank armor, though it has little effect on personnel (the needle just blasts through people as if they weren't there, and since it doesn't splash, it just makes a very small hole). And powerguns, that fire bolts of energy from polyurethane wafers as ammo.
 * The Dresden Files: Kincaid at one point uses Dragonsbreath shotgun rounds to turn his disposable shotguns into flamethrowers. This inspires Harry to read up on other unusual shotgun rounds, including flares.
 * Alloy of Law: Anti-Allomancer rounds. The expensive ones are made out of Aluminum, the cheap ones vary based on target: Coinshot rounds are fronted with ceramics that will keep going when they push on the metal, Lurcher rounds contain ceramics surrounded by metal and fragment when pulled, Tineye rounds are excessively loud, Thug rounds are enormously over-sized.

Live-Action TV

 * Doctor Who: UNIT's final appearance in the old version, following an absence of some years, it was shown that they had got tired of facing Immune to Bullets menaces and developed special bullets to even the playing field. These included teflon-coated armour-piercing rounds for robots and Daleks ("A non-stick bullet?" the Doctor muses), high-explosive rounds for Yetis, gold-tipped bullets for Cybermen, and silver bullets just in case.
 * This continues in the new series, where UNIT uses rad-steel coated bullets.
 * In "Revenge of the Cybermen", the Doctor mentions the "glittergun", which turns Cybermen into gold-plated statues as it clogs their vents.
 * In Kamen Rider Kuuga, a particularly persistent Monster of the Week (introduced in episode 2, finally offed in episode 39, though he doesn't appear in every episode) winds up getting its corpse analyzed to create special ammunition that can actually affect Grongi.
 * In Kamen Rider OOO, Kamen Rider Birth uses a gun which fires Cell Medals at Yummies. Given that the term phlebotinum seems to be a play on phlebotomy (drawing of blood), and that Yummies (and the Greeed who created them) tend to "bleed" Cell Medals, this seems to be a fairly direct invocation.
 * At one point in V|V: The Final Battle, the heroes discover that Visitor body armor is now impervious to conventional bullets. Teflon-coated bullets solve this problem rather quickly.
 * In the Star Trek Enterprise episode "Regeneration", the Borg adapt their force fields to block Earth Starfleet phase pistols after a few shots. The Enterprise's engineers manage to boost the weapons' output, making them effective again ... temporarily.

Tabletop Games

 * Warhammer 40000: has several examples, like Hellfire rounds, shells filled with a mutagenic acid that causes a near-instant and very painful death to anybody unfortunate enough to get hit by one, Dragonfire shells, which explode in a burst of superheated gas and Kraken bolts, which contain cores made of Thunderbolt Iron.
 * GURPS Ogre,: the standard anti-personnel round is "ap-fizz dizzy-doo" (APFSDSDU): armor-piercing, fin-stabilized, discarding sabot, depleted uranium.

Video Games

 * Resident Evil 3: in addition to normal grenade rounds, also has acid, fire, and ice grenades. Code: Veronica also features anti-BOW gas rounds.
 * While we're on the Survival Horror note, the tail end of Parasite Eve features bullets laced with the protagonist's mitochondria. And that's not even touching the fact that the game's main feature is elite gun tweaking to make bullets that freeze, burn, tranquilize, or poison with acid and cyanide. (Then there's the crazy things the guns themselves can do, barring the already-powerful-enough rocket launchers.)
 * DoomChex Quest Game Mod: Originally the flemoids/phlemoids (Whichever you prefer) were immune to conventional weapons. However, the "Zorcher" works by remodulating the dimensional frequencies of the creatures, sending them back to whatever realm they came from. Therefore, no killing the...green...slimy mucus things that want to eat the main character alive, and Ta-Da! It's kid-friendly!
 * Bio Shock: has ammo for weapons ranging from (relatively) realistic things like armour piercing bullets to things like electric shotgun shells, exploding shotgun shells, a flamethrower that also fires liquid nitrogen and electric gel, and a crossbow with fire bolts and bolts that shoot wires. And then there's plasmids...
 * Stars!: has depleted neutronium ammo -- presumably, dense far beyond the bounds of normal matter. (How you deplete neutronium is unknown to modern science.)
 * Jagged Alliance 2 v1.13: introduced AET (Advanced Energy Transfer) ammunition. They pierce armor, but behave like hollow-point rounds when they strike flesh. The developers suggest not thinking too hard about how that works.
 * Singularity: is powered up with the time-warping abilities of "Element 99." Some of the weapons have special abilities because of this (like a sniper rifle that slows down time so you can shoot a moving target) but for most, it just makes their bullets hit harder.
 * Ninja Gaiden: when Ryu used APFSDS cores as arrows, to destroy heavily armored tanks and helicopters. But then, that whole section of the game is an exercise in Refuge In Audacity. There are also explosive arrows for when getting through armour is less important than AOE.
 * In Starcraft, the "U-238 Shells" upgrade swaps out the standard Terran Marine rifle round for one made from depleted uranium. This increases Marines' attack range by 25%.
 * Railgun rounds in Escape Velocity: Nova are stated in flavor text to be forged of metals that are highly conductive but cheap, such as copper and gold. The rounds come in 100, 150, 200, and (with the ARPIA plug-in) 400 millimeter sizes.
 * The Godfather 2 has incendiary rounds as a reward for completing a certain crime ring.

Web Original

 * Jack Yaeger's gun in The Mercury Men fires bullets made of solid light, apparently the only thing that can kill the Mercury men.

Western Animation

 * In Centurions, energy specialist Rex Charger had assault weapon systems that fired missiles that contained... energy-changing stuff. Magnetic shields, light, energy that was absorbed by a gun--the missiles were Techno Babble shells. This meant that they were exactly as powerful as the plot demanded: on separate occasions, Rex blew up a Swirly Energy Thingy and killed a black hole.