13th Age has these for dragons, as expected, but sorcerers have a variation known as the breath weapon spells — Breath of the White, the Green, the Blue, the Black, and the Grave (because the Red ain't much for sharing). The breath weapon rule means that while the spells can usually only be cast once per day, after you cast them, you get a roll at the beginning of each action you take for the rest of the battle to see if you get another use, although you can only roll for one breath weapon at a time. A couple of their Talents, namely Chromatic Destroyer Heritage and Metallic Protector Heritage, make breath weapon spells more powerful, encouraging sorcerers who take those talents to grow into endless volleys of dragonbreath.
Anima: Beyond Fantasy: Dragons of C'iel and Gaira. The former has a breath weapon that consists of feathers of light, that may instead cause the targets to stop the fight, and the latter one made of chains of darkness that end on spikes and can inmobilize their enemies. The game features also normal dragons, that have breath weapons a laDungeons & Dragons above.
Fire Demons can breathe out a cone of violet flame 30 feet long and 10 feet wide (at the base) once every three melee rounds. The flame does 36 Hit Points of damage and has a 75% chance of igniting flammable materials.
Ice demons can exhale a freezing cloud that blinds all inside it and does 17-36 Hit Points of cold damage.
Night Demons can breathe a 15 foot long and 3 foot wide tongue of black flame that causes 60 Hit Points of damage and permanently takes away two points of Constitution.
The Greater Demon Amon-Rha can breathe out a cloud of poisonous gas in a cone 60 feet long and 30 feet wide at the base up to eight times per day. The cloud lasts 5-10 melee rounds and does 11-20 Hit Points of damage per melee round.
Thirteen times per day, the Greater Demon Boak Chaos Hoof can breathe out a 45 foot diameter cloud of chlorine gas that does 21-40 Hit Points of damage and causes any victim with less than 30 Hit Points to choke to death after one melee round of exposure.
Dagonus the Death Dragon, a three-headed Greater Demon, can generate a 180 foot long lightning bolt or 90 foot long cone of flame seven times per day per head.
The Greater Demon Nagandas, Lord of the Sea Serpents, can breathe out jets of high pressure water that do 21-40 Hit Points of damage.
The Greater Demon Shabaleth, the Dread Elf. Once every five melee rounds he can breathe dragon-like flames in a cone 20 yards long and 20 feet wide at the base that do 31-50 Hit Points damage.
The Greater Demon Urandos, the Blizzard Queen. Ten times per day (but only once every five melee rounds) she can breathe out a cone of cold 60 feet long and 30 feet wide at the end. It does 31-50 Hit Points of damage.
The Tarakk is a giant horned lizard/dragon that can breath out a cone of fire 90 feet long and 15 feet wide at the end that inflicts damage equal to its own Hit Points. The fire breath can be used once every three melee rounds, up to four times per day.
Wyvergons breathe out a petrifying gas.
Yellow dragons breathe a deadly nerve gas that either kills or incapacitates victims. It also temporarily blinds any creature in it as well as having a chance for the blinding to be permanent.
BattleTech: Head-mounted weapons are sometimes depicted as coming from where the Humongous Mecha's 'mouth' would be, though they are functionally no different from depictions of Eye Beams or skull mounts. The 100-ton 'Berserker' mounts a flamethower within its Nose Art mouth for terror factor as it approaches with its BFS, and the 'Hauptmann' carries a small beam laser in a cigar-like casing in the mouth.
Chaosium's supplement All the Worlds' Monsters Volume III:
The Baggol has a breath weapon that does 4-24 Hit Points damage with the creature's choice of side effect: sleep, fear, fire or acid.
Balitorr, King of the Earth Elementals, has a breath attack that can turn opponents to stone, usable twice per day.
Dragons
Chestnut/Pearl: its breath weapon is the same as the Dungeons & DragonsWeb spell but lasts indefinitely. Its breath can also be used in reverse to destroy all types of webs.
Hazel/Jade: its breath inflicts paralysis on all creatures in a 70 foot long by 30 feet wide (at the base) cone.
Tan/Turquoise: breathes out flame in a 90 foot long by 30 feet wide (at the base) cone.
The Fire Lion's fiery breath does 8-48 Hit Points of damage to any creature it hits.
The Frost Horror is an elephant-sized white dragon with red eyes. It has a fiery breath that does 13-78 Hit Points of damage in a cone shape 60 foot long and 30 foot wide (at the base).
The Glamdar is a blue-gray monster covered with metallic scales and spines. It can breathe out a cloud of radioactive gas that does 5-50 Hit Points of damage to all inside it.
The Steel Golem has 100 Hit Points and breathes out a 30 foot by 30 foot cloud of chlorine gas three times per day. The entry doesn't say how much damage it does, so assume it's the same as a 1st Edition Dungeons & Dragons dragon and does damage equal to its own Hit Points.
The Hell Sprite is a short two-legged monster with two glowing red eyes. It has a breath weapon that does 2-12 Hit Points of fire damage to all creatures in a cone 10 feet long and 5 feet wide at the base.
The breath of an Ice Mouse does 1-6 Hit Points of damage to a single target.
The breath of a Kendry's Night Demon does 10-80 Hit Points of fire damage.
The Mandadon has the body of a giant snake and the wings and head of a white dragon. Its breath does 10-60 Hit Points of cold damage.
A Mantigon is a cross between a manticore and a blue dragon. It can breathe out a lightning bolt that does 5-60 Hit Points of damage.
The Nasnas is a huge panther-like animal that constantly hunts for and kills dragons and dragon-kin. It has a very useful breath weapon: it negates dragon breath weapons on contact.
The Osta Beast's breath is so foul that any creature breathing it must make a saving throw versus poison or be nauseous for 10-20 minutes and be unable to anything but vomit.
The Perneese Fire Lizard (based on the ancestors of the dragons in Anne McCaffrey's Dragonriders of Pern novels) have a breath weapon that does from 1-4 to 1-8 Hit Points of fire damage, based on the dragon's color.
The Scorpan is a human/scorpion crossbreed. It can breathe out a flood of acid that does damage of 4-48 Hit Points.
The Shock Troll can breathe forth a cloud of poison that does 5-30 Hit Points of damage immediately and causes death within 1-20 melee rounds. It fills an area of 1,000 cubic feet and can be used 3 times per day.
A Flying Turtle has an acid breath attack that can be used three times per day and does 3-12 Hit Points damage.
The Fire Worm does 24-48 Hit Points of damage with its fire breath.
The Wurm Eater is a giant crab that can breathe out acid that does damage of 11-66 Hit Points.
The Dresden Files RPG: Breath Weapon is one of the available powers. The description broadens it so that the power can cover any self-generated projectile, even if it doesn't come from the mouth. This notably includes the Shen demons' use of flaming poo projectiles.
Dragons, of course, are distinguished both lore-wise and mechanically by their breath weapons. The game often tries to assign a unique weapon to new dragon types, resulting in some rather esoteric weapons having cropped up over the years.
Chromatic and metallic dragons are, as with everything else, Colour-Coded for Your Convenience. Red, brass, and gold breathe fire, blue and bronze spit lightning, green breathe corrosive gas, black and copper spit acid, white and silver breathe gusts of freezing air. Most of the game's imitators (including NetHack) follow suit, though different games do not always follow the same color-to-damage assignments as the original (although red is more likely to remain fire than any other).
Metallic dragons have two breath weapons. The second is usually some kind of nonlethal but disabling gas attack: brass dragons have sleep gas, bronzes have repulsion gas, coppers have slowing gas, golds have Fortitude-reducing gas, and silvers have paralytic gas. The second is a straight-up damage attack.
"Secondary" dragon types are where the really bizarre breath weapons crop up. Iron dragons, for instance, breathe molten iron, mercury dragons breathe laser beams, amethyst dragons spit exploding crystals that they can shoot with pinpoint accuracy...
Dragon-based classes often give breath weapons. The most classical example are dragon shaman and dragonfire adept.
Homebrew dragons can get even weirder. There are probably quite a few here. Aside from those there are wing dragons and beige dragons. Wing dragons have the only breath weapon that OSHA (the Occupational Safety & Health Administration) would probably approve as harmless. It's sky painting smoke... that they can telekinetically control... and turn optic black... and then blind their targets by surrounding them in... and then do stuff like slitting the throats of in the dark. Beige dragons have an invisible line of pure elemental ennui that makes you stupider and less interesting as a person.
4th edition dragon breath weapons are technically vomit weapons. The edition also adds the Dragonborn as a core Player Character race, who possess their namesakes' signature attack. The Draconomicon teaches that the magical energy of a D&D dragon's breath weapon is stored in the stomach, not in the lungs; this is what is meant by "vomit weapon". The expelled effect is explicitly magical, though—it is mystical energy, and not a biological by-product as found in some other D&D creatures.
The game offers a substantial number of nondraconic monsters with their own Breath Weapon: Hellhounds breathe fire, as just one example. A popular method of making a "new" monster is to simply slap a Breath Weapon on an existing animal or mythical creature: the Pyrohydra, for instance, is a Hydra that breathes fire!
The 5e a spell, "Dragon's breath" gives spellcasters the ability to give themselves and their allies a similar breath weapon to Dragonborn.
Planescape: The Planes of Chaos boxed set describes the Varrangoin, bats that live in the Abyss. The Type I version breathes out a cone of cold that's 55 feet long and does Hit Points damage. The Type II variety has a breath weapon that creates a ball of fire 10 yards in diameter up to 30 yards away that inflicts 5-30 Hit Points of damage.
Certain "metabreath" feats can allow all these creatures to breathe something different, or even shape their breath. Often abused when one type of dragon is impersonating another...
The Greater Drakes in 2nd and 3rd edition have non-magical breath weapons; most drakes collect or generate a substance in their throat pouch that they can spit at enemies (exactly what it is varies by species; for three examples: the Smoke Drake generates thick smoke, the Muck Drake stores the swampy water of its lair, and the Hive Drake has a nest of hornets living in its pouch).
Certain items, such as specific magic scrolls and the Tongue Stud of Firebreathing, allow their users to use breath weapon attacks.
The game has the dragon template, which of course includes a Breath Weapon. Azhi dahakas from GURPS Fantasy Bestiary are three-headed dragons with a different breath weapon for each head — fire, poison gas and hypnotic gas — and which can use any two on any given round.
GURPS: Magic has various Breathe Ice/Fire/Radiation/Steam spells.
This is one of the many forms that a Blast or ranged Killing Attack power can take in this system.
Dragons and Hydras from the Fantasy Hero Companion can have a breath weapon that is a 4d6 fire Killing Attack, which can badly burn a normal human being.
Also from the Fantasy Hero Companion are clay and metal golems, which can breathe out a cone of fire four times per day.
Hunter: The Vigil: The Ascending Ones' Breath of the Dragon Elixir is a crystalline powder that, when inhaled, allows its user to exhale a cloud of poisonous gases. Its name is based on the older, Classical and medieval iterations of the dragon myth, where the serpents exhaled poison instead of flame.
The iconic spell Firebreathing grants this power to any one creature. Many creatures have similar abilities, especially draconic creatures of the color Red. The ability is so common and iconic, in fact, that when a player says a creature "has firebreathing" it's immediately understood by most experienced players exactly what that means, word-for-word. It's also a fairly powerful ability as well. (Of course, "firebreathing" isn't an official term in the rules, apparently since the designers don't like creating keywords for activated abilities - but it's as close as an unofficial term can get.)
The mage breathed in life-giving air and breathed out death-bringing fire. — Flavor Text for Firebreathing.
In Tarkir, dragons are aligned with all colors of mana, which naturally draws them to other elements. The Green-White dragons, for instance, produce searing beams of light, the Blue-White ones ice, the Black-Blue ones black corrosive smoke and the Red-Black ones bolts of lightning. The only ones that breath fire are the Red-Green ones, which produce unusual green flames.
Dragons have the same sorts of breath weapons they have in D&D — fire for golds, brasses and reds, freezing wind for whites and silvers, acid for blacks and coppers, acid gas for greens (changed to poison in 2nd edition), and lightning for bronzes and blues. Most other types of dragons have associated breath weapons, of course, although these aren't always described in detail beyond their in-game effects — for instance, magma, underworld, solar and vortex dragons have fire (which magma dragons having the option of horking up a glob of lava instead); lunar and void dragons have freezing wind; brine, rift and nightmare dragons have acid; cloud, sky, time, dream and bliss dragons spit lightning bolts; crystal and sovereign dragons have sonic roars; sea dragons can choose between a gout of boiling water and a cloud of equally hot steam; and forest dragons have a hail of rocky shards capable of petrifying victims.
Elder Wyrms have two heads, one of which can breathe a line of electricity while the other breathes a cone of corrosive vapor. Where it gets interesting is when they use their "Impossible Coordination" ability to launch both weapons at once: the electricity from the first head ignites the vapors from the second, resulting in a devastatingly powerful cone of fire.
Korir-kokembes are lesser dragons from the Mwangi expanse that live symbiotically with swarms of arthropods that next in their gullets. As a result, instead of a typical elemental breath weapon, they can vomit out swarms of ants, wasps, or spiders.
Mukradis are monsters resembling three-headed centipedes, with each head being able to use a different breath weapons — one head breathes fire, one spits acid and the third looses lightning bolts. A subterranean variant supposedly exist whose heads all vomit up animated acid instead.
Talisman: Most dragon enemies have a breath weapon, which they use on attacking characters before they enter combat. There is usually a condition that determines whether the character is affected by the breath attack, be it decided randomly with a die roll, based on a character having certain types of equipment in their possession (like weapons or armor), or based on the character's strength or craft scores. While many of the breath attacks cause characters to lose additional life, others may cause them to miss a turn, lose their spells, discard their fate, or anything in between. Some dragon breath weapons even affect other cards or characters that are unfortunate enough to share the same board space as the dragon.
Varanae generic RPG supplement Monstrum 1: Eurytion are a race of giants that can breathe out a flame attack up to 30 yards away once per minute. The flame does an amount of damage equal to the Eurytion's Hit Points.
The Great Unclean Ones, greater daemons of Nurgle, god of decay, can open their mouths to unleash a torrent of fecal matter, mucous, garbage and maggots. As bad as that is, the crap they squirt out is magical and full of the essence of decay, so any victim of this attack will either rot away to nothing or mutate into a daemon.
Orks have a spell called Psychic Vomit. You can guess which of the caster's orifices it comes from.
Tyranids, a Swarm of Alien Locusts that makes strict use of Organic Technology, includes bio-plasma as part of its arsenal, which allows the swarm's warrior forms such as the Carnifex and the Hive Tyrant to hork up balls of superheated ionised gas from their mouths.
Dragons have the usual array of breath weapons — fire and toxic gas are the most common, but some variants have ice, lightning, acid and so on. More unusual examples include carmine dragons, which breathe the essence of the magic of death and cause their victims to age and wither into nothingness; toad dragons, who breathe corrosive gas that melts flesh and metal alike into slurry; and shard dragons, which breathe out a fog that induces terrifying visions when breathed in.
Trolls have a breath weapon of sorts where they can vomit out a glob of stomach acid so strong it can melt steel.
Warhammer Fantasy Roleplay: The Breathe Fire mutation, one of the mutation options in the 2E Tome of Corruption, allows its bearer to spit or exhale flame. One level of it gives the ability to spit a single fireball for up to four yeards, two levels make the fireball explosive and double the range, and three replace it with a gout of fire.
. Aside from those there are wing dragons