Sapping the enemy's will to fight is always a good idea; the Emotion Bomb can make it quick and easy (barring any inconvenient Heroic Willpower, of course). Victims of despair begin to think of themselves as worthless, of the enemy's victory as inevitable, and of any attempt at resistance as utterly pointless.
Anime & Manga
Perona's Negative Hollow attack in One Piece sends a ghost through the opponent that leaves them crippled with despair and depression (often wishing they were, say, some seaweed) though only lasting a few seconds. Usopp, who already lacks self-confidence and spends a lot of time in a funk anyway, is immune to it.
The elves in Discworld's Lords and Ladies seem to include this in their general aura of "glamour". How could something as clunky and utterly inadequate and human as you ever hope to defeat an elf? You don't even deserve to exist next to, much less rebel against, something so perfect as an elf. The Auditors also fight like this when incorporeal, making people think that fighting them is pointless because there's nothing really there to fight.
It's implied that a slow-acting version of this mixed with mundane counterintelligence got to Denethor of Lord of the Rings (book only), finally driving him to an attempted murder-suicide. This is why you shouldn't engage in direct psychic contact with the immensely powerful Big Bad (Denethor has one of the palantíri, or Seeing Stones, like the one that Pippin took from Gandalf and looked in).
However in both the books and films, the Nazgűl have this power, mixed with fear.
Harry Potter's world has Dementors, who guard the prison of Azkaban. Dementors sense and feed on the positive emotions, happiness and good memories of human beings, forcing them to relive their worst memories. It is notable that Dumbledore is against the use of Dementors, considering them cruel and unusual punishment (as well as a natural fifth column for Dark wizards.)
Averted in The Bones Of Haven. Initially, the Brimstone Boys' very presence seems to have this effect on the Special Wizardry And Tactics team's sorcerer. It turns out he was faking, so as to catch the Boys off-guard.
The Lord Ruler of Mistborn: The Original Trilogy uses his powers of Soothing to deaden the emotions of anyone within about a mile radius of him, sapping them of the will to resist him (though a skilled Mistborn can counteract the effects to a degree by Rioting the emotions of those in his or her immediate vicinity). Later on, Vin learns to do a similar trick, though because she's much weaker than the Lord Ruler she can only effect a few people at a time.
In Saberhagen's Books of Swords series this is what the Tyrant's Blade (AKA Soulcutter) does. When it is drawn from its sheath everyone in a 250m radius including the wielder is struck with such crippling despair that most will be unable to summon the will to do anything, even eat when food is provided.
This is The Mule's favorite weapon. Used broadly, it makes enemy armies surrender. Used narrowly, it is the most horrible death possible. He can produce other emotions too, such as loyalty and confidence for his own servants.
The Nameless one from the Brimstone Angels novel The Adversary is a Chosen of Shar (goddess of darkness, nihilism, and entropy) and carries a permanent aura with her that saps life and hope from anyone in the vicinity. Prolonged exposure is sufficient to reduce Sairche (who in addition to being a poised, composed villainess is a litera devil) to a shivering wreck.
The aptly named Despair Squid of Red Dwarf causes hallucinations in its victims that are so terrible that the victim commits suicide.
According to the Ninjormon, ninjanaries have to fight a sad dragon to get their mission calls.
The Dungeons & Dragons spell crushing despair does not disable its targets completely, but is one more avenue (along with spells like cause fear) to whittle away at an opponent's combat effectiveness until he can't hurt anyone, defend himself, or even run away.
Morag uses one of these to turn Aribeth to the dark side in the original Neverwinter Nights campaign
Hugely popular with the Obviously Evil set, an aura of terror can have similar effects to that of despair, but usually more immediate and obvious. It tends to cause less passive slumping and more panicked fleeing. Or panicked A-Team Firing. Or panicked freezing-like-a-deer-in-the-headlights. Just as long as they're panicking.
Anime, Manga, & Light Novels
Causing paralytic fear is a common effect of very powerful ki-aura in many manga and anime. In some series, it can get so bad that the weaker person actually suffers a hallucination of taking a killing blow for a split second... assuming that they don't actually die from the pressure of the aura.
Zophise, the Big Bad of a story arc of Gash Bell, is able to manipulate the demons of a thousand years ago into fighting for them by making them believe that, after being freed of their stone curse, that Zophise can return them to stone at will. After spending 1000 years utterly immobile, that fear is enough to get them to do anything for him.
In a rare heroic example, this appears to be what Dhienalia of Heroic Age does to Phaeto when she psychically attacks him. His mind is flooded with images of terrified humans, he retreats very quickly, and for the rest of the series has a crippling fear of humanity that causes him to act irrationally. (Unfortunately for Dhienalia, serving as the conduit for all that fear is not healthy for a person's psyche either.)
In Naruto when confronted by Orochimaru in The Forest of Death during the Chuunin Exams, Sasuke and Sakura are paralyzed by fear from just one of his Evil Glares. Sasuke had to stab himself in the leg with a kunai in order to "wake up", grab Sakura, and escape before Orochimaru's kunai could finish them off (right in the forehead!).
The main method of Mind Rape used by As Nodt in Bleach. Said character's arrows inject his opponents with fear, causing them to be literally scared to death. It's so effective that it sends Byakuya Kuchikitotally over the edge.
The air didn't grow cold — it just stopped. Completely.
In the X-Men Legends series, Emma Frost can do this to every enemy in her range, making all of them bolt. This only makes it so that you have to run after them to take care of them before the effect wears off.
In Sonic the Comic, Chaos did this. It was, however, resistable, as two characters were able to get close to it this way (Sonic achieved it by concentrating on rage).
In "Pokémon Mystery Dungeon Journal" Jaroda and Lady Christine have access to an Aura technique called Fear Aura, which Jaroda uses to force Heath to take a job for him.
The Ringwraiths in Lord of the Rings are constantly surrounded by a combination of this and Despair. Hardened soldiers break and run in their presence, and it's strongly implied that Éowyn is only able to stand up to the Witch-King because she's been living in constant despair for years. She's used to it.
The Army of the Dead has the same effect, either because of inherent magic or just the natural reaction to seeing a huge horde of nasty ghosts. In the book it's left ambiguous whether they can actually hurt people, but they don't need to because the fear is enough. In the film, because this sort of subtlety is hard to express in a visual medium, they kill people by more direct means, but their appearance still sparks a Mass "Oh, Crap!" from the enemy.
In Night Watch, Lord Winder is frightened to death by a young Havelock Vetinari.
The myrddraal of The Wheel of Time emanate an aura of fear, especially along their line-of-sight.
The Fury Twins Phobos and Deimos of the Whateley Universe. Each has a fear aura. When they merge into a single creature, the fear aura gets so bad they warp reality in the vicinity. Unlike most characters in this category, they're not evil, and in fact they are receptive empaths so they have to feel the fear of everyone around them, which they don't like.
A side effect of the drug used to commit the murders in Sherlock Holmes in the Adventure of the Devil's Foot was that it caused a paralyzingly intense sense of fear.
Many of the more powerful monsters in Fablehaven had fear auras that paralyzed any mortal that came too close to them.
Live Action — Film
This is how Scarecrow, and Ra'as Al Ghul, who is directing him, plans to destroy Gotham in Batman Begins. His cronies dump the fear drug into the water supply and vaporize it to drive a large chunk of the city insane.
One of these was used in the Doctor Who serial The Sun Makers by the evil tax-gathering government to control the human populace. The Doctor inverts the technology to make people angry instead.
Charmed gives us Barbas, the Demon of Fear, who is able to read the worst fear of his targets, and make them believe they are living it through illusions. He's even able to kill his victims his way.
His flipped-universe counterpart is a hippie who lives in a beautiful garden and inspires the emotion of hope.
Kamen Rider Double's Big Bad, Ryuube Sonozaki AKA the Terror Dopant, is able to generate a field that causes anyone caught within it to suffer from intense fear (as in, curled up in the fetal position and screaming like a madman). He can also turn his Nice Headdress into a Kaijuu dubbed the Terror Dragon. Even without transforming, Ryuube himself can instill a degree of degree of terror in those around him.
Various spells such as Scare and Cause Fear (the reversed form of Remove Fear) can temporarily frighten an opponent.
The 1st Edition psionic power Telempathic Projection allowed the user to implant fear in an opponent's mind.
Certain creatures have the ability to cause fear in opponents, such as androsphinxes (roar), beholders (one of their eyes), some demons, devils, dragonnes (roar), mummies and satyr (by playing their pipes).
All dragons in some editions are constantly surrounded by an aura of fear that sends any low-level character into panic. They can, however, turn it off for a brief time. A few other monsters also have fear auras, such as liches.
In 3.5 and Path Finder, it's not a magical or psionic effect: dragons are just plain scary. Mechanically, if a dragon with greater hit dice than you does anything threatening, you have to roll your save.
A very popular ability in Warhammer and Warhammer 40,000 is the ability to inflict fear (or, worse yet, terror) on the enemy.
Fear effects are a common game mechanic in World of Warcraft and other MMORPGS, with afflicted players and monsters running randomly around the place. Many a player has cursed this when feared right into the next bunch of monsters, and it used to be that you could be scared right off a cliff!
Befitting his status as the Lord of Terror, Diablo is able to sow panic among his enemies and, as a bonus, is utterly incapable of feeling fear himself.
The Fear Point in Immortal Defense may count. It slows down enemy targets, but represents the player character's own anxieties and its effect is probably just caused by its environment's metaphor tangibility. If fully upgraded, it "panics" and fires blindly.
The Elder Scrolls has the aptly named "Fear" spell. It makes the target flee from anything hostile to them.
A Pokémon using the ability "Intimidate" scares the opponent so badly it lowers its Attack just by showing up. Naturally Gyarados has this ability.
There's another ability called "Unnerve", which prevents enemies from using their held Berry, and can be used by Pokemon like Mewtwo, Tyranitar, andJoltik.
A weaponized version is used in the attack Dark Pulse, an attack in which an aura filled with horrible thoughts and emotions is fired, which may cause the target to flinch and not attack for a turn.
In the Pokémon Mystery Dungeon series, there's an IQ skill called Intimidator(not to be confused with the above Intimidate), which can scare enemies so badly that they won't attack for their turn. High-end bosses and certain enemies in later dungeons use this, which can be frustrating for the player. But if the player picks the right Pokemon and is patient enough to raise its own IQ level, you can also use it, in a rare heroic version. However, this skill doesn't work if the enemy uses a long-range attack, even if they're right next to the the user.
The Witcher has a literal example in the King and Queen Trick Bomb, which evokes terror in those affected.
Definitely more a distracting tactic than an incapacitating one. When Love Is in the Air, no one's mind is on their job. If it's possible to direct the emotion at yourself, you can even use it as the lead-in to More Than Mind Control, or just make sure people are reluctant to attack you.
General: If there are any Horny Devils who can't do this, they're very much in the minority.
Anime, Manga, & Light Novels
The Girl in the Dress from A Certain Magical Index has a certain psychic ability, Measure Heart: she can make any person feel towards her as if she was their most beloved, shattering their will to fight, giving them an extreme guilt complex and mercilessly confusing their feelings. However, she makes special note of that it only works on specific enemies: Those that wouldn't harm their beloved when betrayed. That is why she stays the fuck away from Accelerator.
In Axis Powers Hetalia, America invents a "love gun" which he believes would make enemies shot with it fall in love with each other and leave them unwilling to fight.
Salamander, a low-level villain in the first issue of Fairy Tail had such a spell, which he used to entrance young women and attempt to sell them into slavery.
Yu-Gi-Oh! played with this by having Mai Valentine (Mai Kujaku) use the "Shadow of Eyes" spell to entrance monsters to attack, having their power drastically reduced by her "Mirror Wall" trap and be destroyed in the process. Yami Yugi cleverly (and in defiance of all game rules) subverts this by summoning "Mystical Elf", a female monster, in defense position.
GX also plays with this trope by having Rei Saotome (Blair Flannigan) initially run a deck focused on dropping Maiden Counters on her opponent's monsters and having them serve her. While the way Judai (Jaden) trumps this is within the boundaries of the rules, it still focuses on Burstinatrix being female, which is overall irrelevant to the duel at hand.
The main power of Venus from Agents of Atlas. It gets them out of a lot of fights, as suddenly everyone is either gaping at her or thinking of their own love.
The finished product in Perfume causes such powerful feelings of love and desire that it triggers an instant mass orgy at the scene of its maker's intended execution. In the end, an overdose of the perfume causes a mob to gather around and devour the protagonist.
In Harry Turtledove's Worldwar series, the female aliens go into heat when exposed to ginger (and their pheromones drive nearby males into a mating frenzy). So the clever earthlings use ginger bombs.
In Saberhagen's Books of Swords series, the Mindsword, when drawn from its sheath, causes all within 250m including gods to become fanatically devoted to serving the wielder.
Vampires in the Ringworld books are non-sentient hominids that give out a pheromone that can override any non-sex-related thoughts in the victim while the vampire feeds.
Whateley Universe examples: Fey has a glamour that does this even when she doesn't want it to. Carmilla can evoke a lust aura that's overwhelming. And Cytherea likes to use her lust aura to get her way, since she's really the avatar (or something) of Aphrodite.
Live Action — TV
The "gay bomb" is referenced on 30 Rock, when Jack Donaghy uses it on the Joint Chiefs of Staff in order to get fired and return to GE.
A less-publicized race on Star Trek: The Original Series was the Deltans, a species that looked like hairless humans (they had eyebrows and eyelashes, but male and female were both completely bald). They naturally produce universally-recognized pheremones, and when in Starfleet have to take pheremone-production-inhibitors to keep everyone (of either gender, apparently) from trying to have sex with them.
In the first episode of Torchwood, Owen is shown using some sort of alien breath spray that causes anyone who gets a whiff of it to want to jump him right there and then.
The following episode has an alien that possess a human invokes Death by Sex coupled with driving people around it mad with lust.
Villains And Vigilantes adventure Devil's Domain. The Devil has the power to affect the minds of all creatures within a certain radius and make them love him.
A Valentine's Day seasonal event in World of Warcraft has someone do this worldwide so that everyone will be moonstruck and distracted for some attack that's never followed through on. He has help from some naive individuals who really just want to "help ease the awkward rituals of courtship".
The Pokémon move "Attract" gives a chance that Pokemon of the opposite gender will become too smitten to attack.
Baroque has Lust as a status ailment. It makes all enemies and treasure chests look like women (and the women all look the same).
The SCP Foundation has SCP-252, a literal "Gay Bomb", that does exactly as described, with a cloud of pink smoke.
Ember in Danny Phantom made Danny fall in love with Sam to distract him from fighting her.
In a strange Real Life example, during a "no criticism allowed" brainstorming session the US Army speculated on chemicals to provoke widespread homosexual behaviour among troops. Found here with other lovely ideas that never got past the brainstorming point. Nevertheless, it has found its way into pop culture (see above).
Despite being one of the least subtle emotions, anger requires perhaps the most finesse to weaponize effectively. Afflicting someone you're already fighting with Unstoppable Rage is... unwise. (Though it can be used to your advantage if you remove their ability to think straight, or at least get them pissed enough to charge in without taking time to plan—some video game foes can cause absolute devestation by inflicting the Berserk status (while others can have their ability to inflict damage or defend themselves completely nullified). But if you can deploy it from a safe distance before or between fights, especially if their alliance against you is already a case of Teeth-Clenched Teamwork, it's amazing how much trouble can be caused.
This is its own subtrope, Hate Plague, so examples go there.
Other or Multiple:
Other / Multiple examples
Anime & Manga
In Fairy Tail, the Moe stellar spirit Aries uses Wool Bomb attack, which overwhelms her opponents with comfort.
The Psycho-Man, a villain from Marvel Comics, has three settings on his emotio-caster: Fear, Hate, and Doubt (the last of which has similar effects to Despair, but is less likely to produce suicides). Usually he is a serious villain who uses the 'caster to Mind Rape his foes, but on one occasion he attempted to get the rather stupid "hero" Drax the Destroyer to do his bidding and was brought to lament that he needed some new settings on the thing,—hate made Drax lash out at everything including him, while fear and doubt made him cower.
Wonder Woman has an aura of truth, such that it's nearly impossible to lie to her face even when she's not using the magic lasso on you, and weaker minds are liable to just start spilling their guts from sheer proximity. Some writers extend this into a sort of aura of trust, making people calmer and more amenable in her presence to a supernatural degree even beyond what you'd expect from a hero of her stature. Genocide, a recent new foe of Wonder Woman's, being an evil frankenstein version of herself, has traded in the aura of truth and trust for the more standard villainous aura of despair and loathing.
The Seven Deadly Sins from The DCU are demons who can make people fall under the influence of their respective sins. One villain Sabbac briefly merged with all seven demons and gained their powers. The first thing he did was to use Lust to make a prison complex have a massive orgy just for kicks.
In the Firefly fanfic Forward, all of the above and more are used as weapons by the Inducer-type psychics, which are psychics who can manipulate human emotions. Lust, fear, and despair are used alternately on River when she confronts one of the Inducers, and Hate Plague is used on a bystander to make him shoot and critically injure Mal.
The Ilivais units in Ilivais X (especially the Phonos Weapons) tend to utilize emotion as a control scheme, at the very least. The Phonos Weapons and their pilots have ridiculously strong Drive Cores, and all of them except for Iriana have been reduced to near Soulless Shells that only live to feel their set emotion. Iriana has a wierd thing that's caused due to X's Drive Core being essentially a really powerful version of the standard, and uses this because she's trying to become an Emotionless Girl instead of a Love Freak. This at leasts partially explains why she isn't as good at piloting it as Mille.
Flinx, main protagonist of the Humanx Commonwealth universe, by Alan Dean Foster, has empathic powers that were originally sense-only, but received an upgrade in Flinx in Flux that allowed him to fully access his latent projective powers. He has used this ability to induce catatonic fear and/or despair in his enemies, at one point immobilizing a youth gang simply by exposing them to a glimpse of his personal angst. In Reunion, he uses his powers to seduce an employee of the Terran Shell complex in order to gain access to restricted data, and manipulates the computer itself.
The Gubru in The Uplift War have spheres which broadcast signals which produce certain emotional responses in anyone who gets too near. Fibbin, one of the main characters, encounters one set which broadcasts fear, and one which broadcasts self-consciousness. Fortunately, neither set is a match for a determined neo-chimp "with delusions of adequacy".
In Startide Rising many psi-weapons are mentioned in the massive space battle happening overhead. The Streaker crew use a psi-bomb as a distress beacon. And the Karrank% unleash a psionic assault that temporarily disorients every non-cetacean sophont in the system, the humans are less effected than most since their brains have some similarity to their dolphin clients.
The Shamer Chronicles by Leene Kaaberboel has at its center two women who are Shamers. They can make people feel buried shame by looking them in the eyes. Conventionally in their society, it is used to find out if an accused is guilty or not, and to make criminals repent on their behaviour. The books also shows it backfiring in several ways.
Firecrafters in the Codex Alera series can inflame the emotions of others. Senators and Lords of the realm that can firecraft generally use this ability during their speeches to influence the listeners. Also, Earthcrafters can create lust, which many exotic dancers use to their advantage - though be able to throw your clientelle farther than you trust them doesn't hurt, either!
While politicians use firecrafting subtly, it goes Up to Eleven. In the first book Count Gram creates a fear strong enough to drive back a barbarian horde, and Gauis Sextus can knock entire legions of veteran soldiers unconscious through sheer mind-breaking terror.
knock unconscious hell, some of them died from it!
Watercrafters have a lot of trouble turning off their psychic sense, such that cities can be actually painful for strong watercrafters from the steadholts. It's also a great way to neutralize them in a fight - just give in to a strong emotion like panic.
Tavi takes out a notably-insane expert swordswoman by using his watercraft to figure out which taunts would be most effective, causing her to lose her cool and make mistakes.
This is the schtick of the White Court vampires in The Dresden Files. The most common emotional affinity is lust, especially among House Raith, which is why they're often called succubi and incubi. Other branches specialize in fear or despair. (Though, interestingly, real, pure emotion can actively injure them; True Love burns lust-feeders, for example) In addition there's, Vittorio Malvora: because he decided to do some finagling outside of the traditional Planet of Hats line, he has the ability to use despair, plus lust, plus fear, all at the same time. It takes the Heroic Sacrifice of a freakin' fallen angel to keep it off Harry.
Worm has two heroes who use this, and two villains:
Glory Girl can create an aura which causes awe in those around her — awe which tends to manifest as fear in those opposing her.
Gallant fires beams which induce random emotional states in those he hits.
Cherish, his daughter, can do similar things, though non-permanently and at a longer range. She uses it to drive people to suicide.
The Protege in Brennus continually projects mind-breaking shame into the minds of everyone within his range — which covers sixteen square miles. The closest anyone has gotten within six years was five hundred metres, achieved by a metahuman with a supposedly invincible mind shield who subsequently went insane. Thankfully, the Protege also hasn't moved in those six years.
Live Action — Film
The "blamethrower", from Mystery Men, produces not so much Anger as petty bickering.
The Hitchhiker's Guide to the Galaxy movie has a "Point of View" gun, which forces the person hit to suddenly understand the wielder's point of view. Generally just distracting, but utterly incapacitating when Marvin uses it, as you can imagine.
The Force power known as Battle Meditation works by bolstering the confidence, courage, and such of the practitioner's allies while at the same time sapping the enemy's will to fight and causing despair and a huge morale drop. It's a very difficult and complicated power, and is very rare; users include Oppo Rancisis, Bastila Shan, and Lord Kaan.
Live Action — TV
The Eureka episode "Alienated", has several characters unknowingly hit by an experimental beam that causes extreme paranoia, while watching a movie about an Alien Invasion. They kidnap a visiting senator, who they're sure is being controlled by an alien.
Used comically in Get Smart where Maxwell Smart (Don Adams) and Ozark Annie (Carol Burnett) are escaping from a KAOS lab. They're developing airborne gasses that instill fear or lust — but so far only able to affect females. The two flee into a room with the first gas, and Annie dissolves into horrified shrieking fits at Max. She runs into the next room, Max cautiously pursues her — and she's become an aggressive, heavy-breathing vamp, to his alarm.
There are a bunch of emotion-affecting spells, including the one actually named Emotion. (That spell includes Despair, Fear, Love and Rage)
Sympathy and Antipathy are two other good ones. Cast on a place, they make you very strongly want to stay there, or get out as soon as possible. Cast on an object, they make you either covet it and obsess over possessing it, or want absolutely nothing to do with it. Furthermore, they only affect specific beings determined when you cast the spell, leaving all other beings unaffected.
Tasha's Uncontrollable Hideous Laughter. It not only incapacitates the target, but also weakens their muscles for a while after they calm down.
In 1st Edition the psionic ability "Telempathic Projection" could send an emotion to a target creature.
The Habbalah from In Nomine are able to impose anger, hatred, depression, love/attraction, fear, or nearly any other emotion upon others, they can also impose "emptiness" which is essentially a state of total emotionless apathy. However if the target successfully resists the emotions will sometimes backlash upon the demon, who can either accept them, and be affected by their own power, or absorb them and eat dissonance. If the demon is subjected to his own emptiness, though, there is a small chance that he may instantly realise he is a demon... since Habbalah by default are deluded into thinking they are angels.
The Psychic Powers sourcebook for GURPS includes a literal emotion bomb—when it goes off, everyone in range experiences the emotion preset into it. The Mind Control skill can be taken with an "Emotions Only" limitation, and the Terror advantage produces fear or "awe".
ParanoiaTabletop RPG. 2nd Edition changed the Empathy mutant ability so that the user could project his own emotions onto an opponent.
Changeling: The Lost offers several Emotion Bombs to the members of the Great Courts. Each Court (Spring, Summer, Autumn, Winter) has a Fleeting [Season] Contract list centered around manipulation of the Court's ruling emotion (desire, wrath, fear, sorrow). In addition, high-powered changelings have the ability to inflict bedlam, which hits everyone in the immediate area with an intense dose of an emotion.
Geist: the Sin-Eaters likewise has various ways to make this work through the Passion Key. The Passion Boneyard allows a Sin-Eater to enter a trance and assume control over an area, where he can manipulate the emotions of everyone therein (and gain benefits when they act towards a certain emotional resonance). The Passion Curse, on the other hand, hits a target with an uncontrollable burst of the Sin-Eater's choice of emotion... and higher levels make it spread to everyone the target touches.
Khorne of ''Warhammer 40,000 has this for his followers, particularly in the World Eater Chaos Space Marines. Though most of them uderwent voluntary lobotomy beforehand.
More to the point, Slaanesh is the Chaos god of lust, pleasure and emotion and experience in general as long as it can be experienced to excess. Inflicting overwhelming emotion on people is both a reward for worshippers and attacks on non-worshippers. As far as Slaanesh is concerned, there's really no difference.
Nurgle is also considered the god of despair and other associated negative emotions. However, there tends to be more focus on disease and death, with the emotion side of things generally being a side effect rather deliberately used as attacks.
In World of Warcraft, the warlock class used to have a spell called Curse of Recklessness. It would drive the target into overconfidence, making them immune to fear effects (and ordinary fleeing, if an NPC) and hit harder but causing them to drop their defence (reducing their armour stat). The spell was recently removed and the armour reduction effect combined with another curse.
The Sha in the latest expansion have this power and use it liberally to their advantage when they lack the power to simply manifest and attack things. The Sha of Anger will Emotion Bomb a village of nomads and send them all into a blind rage directed at anything nearby for any possible reason, Despair will bomb its opposition into depressed lethargy, Doubt will bomb its foes into frantic indecision, and Fear will bomb as expected and has even managed to mobilize an entire civilization into military action by instilling fear for their lives in the empress and her drones.
The Elder Scrolls has the Illusion spell "Calm". The spell causes the target to lose hostility unless they are attacked again.
Occurs in Metal Gear Solid 4. When Liquid shuts off SOP the first and second time, the soldiers affected immediately experience all the emotion the system had prevented them from feeling. This involves such graphic displays as soldiers unable to stop laughing as they beat the shit out of their comrades, and other soldiers simply killing themselves as fear and sadness overwhelms them. Most become brain-damaged from the extreme emotional trauma they endure.
Similarly, Snake himself can get four kinds of "Emotive Ammo": crying, screaming, laughter, and rage. Crying makes them drop their weapons and break down in tears, screaming makes them flee in terror, laughter turns them insane and makes them fire on allies and enemies alike, and rage makes them rush the enemy in a way that would make Leeroy Jenkins proud.
At least four Touhou characters are known to directly manipulate emotions. The Prismriver Sisters do so through Magic Music: Lunasa induces depression, Merlin induces manic delight, and Lyrica neutralizes feelings altogether. Meanwhile, in former Hell, there lives a Green-Eyed Monster who can inflict her jealousy on others (and frequently does, since she can't travel freely and is mad with envy for those who can, driving her to attack them).
Literally used in Video Game/Psychonauts with the Confusion Grenade, which manifests as a green question mark of psychic energy before being primed and thrown by the player.
In Higurashi: When They Cry,Hinamizawa Syndrome is at least as much a Fear/Paranoia Plague as a Hate Plague. Although the characters start attacking each other, rather than being motivated by outright anger, frequently, it's a poorly-conceived self-preservation method. Keiichi in Onikakushi-hen in particular comes to mind.
Magus of El Goonish Shive can't cause or change emotions, but he can strongly amplify existing ones, causing people to act on what they are feeling at the moment. It doesn't always work; he was first seennote 1 The main cast can't see him, only the reader and a few othersnote 2 It's implied it was actually used, unseen, much earlier on Tedd to make him zap Elliot trying to amplify Ellen's impulse to zap Elliot with her Gender Bender beam, but she resisted it and zapped Tedd instead before passing out from the effort of resisting the impulse.
Freya's "vybe" power in Magellan falls into this category. In a more benign application, she can make a large group of people collapse into helpless laughter, a good way to break up a fight. In more desperate circumstances, though, she can do a "full-spectrum vybe" which apparently makes someone experience every possible emotion simultaneously at full force, enough to render them catatonic for hours or days.
Wayward Sons: Frodaity can do this to anyone. She's used it to make people pass out from lust (directed at her), and caused sadness in a couple of enemies so they couldn't fight back (though that was a staged fight).
Sweet Sorrow, an emotion manipulator from the Global Guardians PBEM Universe, concentrates on the darker emotions. She once made a successful escape by making a crowd of innocent bystanders both terrified of and furious with the superheroes trying to capture her.
Western Animation — TV
The Kim Possible episode "Emotion Sickness" has both Kim and Shego accidentally implanted with emotion-altering computer chips, run off a remote-control device which then gets mistaken for a video game...
Two of the Rahkshi from BIONICLE have this power; Turahk triggers fear and Kurahk triggers anger. Makuta Vamprah also wears a Mask of Hunger, allowing him to feed off emotions and other metaphysical things (like energy or a person's goodness).
The Adventures of the Galaxy Rangers episode "One Million Emotions" had the team seeking to recover a stolen "sensation doll" created as a piece of art by an extinct alien culture. Anyone who made direct contact with the doll would be deluged with "one million emotions" ALL AT ONCE (or as Goose called it, "the emotional electric chair"). One of the thieves who touched the doll was reduced to an insane wreck. note He got better in later episodes, though.
An episode of Aladdin: The Series, "The Flawed Couple", had a Villain Team-Up between Abis Mal and Mecanicles involving magical stones that could alter people's moods. Aladdin managed to break the fear one by focusing on the fact that Jasmine was in danger.
Ren and Stimpy - Stimpy creates the Happy Helmet for Ren, in the mistaken belief that Ren would want to be happy.