Invulnerable Horses

In any combat situation with people riding horses on one side, and ranged weapons on the other, some of the bullets (arrows, etc.) are going to hit the horses. After all, real bullets don't have anyone's name on them, they're addressed "to whom it may concern", and a horse makes a mighty big target. It's pretty inevitable that some of those horses are going to get hit and fall down, probably further injuring themselves.

The problem is this is very hard to fake in live-action film and TV barring CGI or similar advanced effects. Training a horse to fall down on cue is hard and training a horse to fall down at a gallop is nigh-impossible. During the so-called Golden Age of Hollywood horse fall stunts were often done with tripwires, often (but not always) with fatal results. Actually shooting a horse is, of course, cruel, expensive, wasteful, and probably illegal, but is sometimes done where the law doesn't prohibit it.

The result is that you can watch dozens of Westerns and never see a horse get shot, no matter how many riders are shot off of them. Because people tend to be sensitive to cruelty against horses, this trope also appears in non-live-action fiction.

As this trope is very common, the examples on this page favor aversions.

Anime and Manga

 * Completely averted in Berserk, where not even horses are safe from being killed horrifically.s
 * No horse is safe in Sword of the Stranger, especially evident in one gloriously violent battle where one fighter slices off a horse's legs mid-run to bring down his opponent.

Comic Books

 * In the 1950s Western tale "The Unmasking of Johnny Thunder", Johnny is trying to get at a villain. He is entrenched at the top of a hill, so Johnny can't easily shoot him or get near him without being shot. So, Johnny deliberately falls off his horse, leaving one foot in the stirrup, so the horse can drag him to the top of the hill. Johnny is shielded by the horse and the fact that he's approaching the villain feet-first. It apprently never even occurs to the bad guy to shoot the horse.

Film

 * Averted in Braveheart in a rare moment of historical realism; the horses get as much of a nasty shock as their riders when the Scots down (historically nonsensical) taunts and pick up very much more lethal spears. The depiction was so graphic that the film-makers were actually investigated by authorities to see if any animal cruelty had occurred. (For the record, it hadn't.)
 * Averted in the 1989 Henry V. During the Battle of Agincourt, several horses (and their riders) are brought down in graphic fashion.
 * Averted most recent East Asian movies, because they actually have very decent animal trainers, but also because their horse resources are many and the one or another dead horse doesn't bother the company too much.
 * Averted via CGI in the Lord of the Rings trilogy.
 * Averted in Lonesome Dove.
 * Played with in The Magnificent Seven. Britt shoots a bandit off his horse at long range. After Chico compliments him, he demurs: "I was aiming for the horse."
 * In the big fight scenes, however, there are several instances of horses falling down from being shot, or being dragged down. They appear to be well-trained stunt animals.
 * In both film versions of True Grit, Rooster's horse is shot during the final shootout and subsequently collapses on him, trapping him underneath it.

Literature

 * Averted in P.C. Hodgell's Chronicles of the Kencyrath series, especially in volume 6, Honors Paradox.
 * A Song of Ice and Fire's battle scenes have numerous descriptions of people having horses cut from under them, and even attackers deliberately targeting them. Don't tell that to Sansa Stark, though, she's disillusioned enough as it is.
 * In the Dresden Files, Harry finds himself facing down the Knights of the Summer Court, mounted, charging him, and very angry. The Knights are all of a significantly higher caliber of magic than he, so he can't just blast them. He stops their charge by averting this trope, and raising an invisible wall about two feet high. The fall doesn't kill the Knights, but it negates a huge advantage.
 * Averted in Twenty Years After, the sequel to The Three Musketeers, when the musketeers frequently force their horse to rear up and take a bullet shot at them. At least one character has a horse land on his leg, but fortunately is not seriously injured.
 * Averted in Robin McKinley's The Hero and the Crown, in which a valuable warhorse is gravely injured (it's said that he should have been mercy killed, but he was the king's and generally a Cool Horse, so the army takes an extra forever to get home so they can go at his pace). Said horse's eventual (very, very eventual!) rehabilitation is a major plot point.

Live Action TV

 * Averted and discussed in the Firefly episode "Heart of Gold." Before The Siege at the climax of the episode, Mal advises the whores to shoot the man, not the horse, because a live horse without a rider will be a distraction to the enemy, while a dead horse is cover. In the aftermath, you can see some dead horses on the ground.
 * Averted earlier in the series when a Villain of the Week tried to hide behind her horse during a gunfight. Mal simply shot the horse and dropped it on top of her.

Mythology

 * Justified in The Iliad, where Achilles' two horses are actually immortal.

Tabletop Games

 * In Warhammer Fantasy Battle ordinary horses (and most other similar sized mounts) are effectively invunerable; a mount has its own attack but in combat only the rider can be hit and if he is killed then both rider and mount are removed. Thus it is impossible in the rules to for example unhorse a knight and have the knight stick around and fight on foot.
 * Averted by the "dragoon" unit type in War Machine, which starts out as a cavalry unit. After it takes a certain amount of damage, it becomes a footsoldier (with the player actually replacing the "mounted" miniature with the "unmounted" miniature).

Webcomics
"[Vaarsuvius] "Thrice-cursed Spell Resistance! It's almost like the universe is trying to deliberately force some form of arbitrary equality between those of us who can reshape matter with our thoughts and those who cannot." [Soldier] "Zap the horse, then." [Vaarsuvius] "Why? It hardly seems to be doing that much-" [Soldier] "So he can't use his mounted combat feats on us Hurry!""
 * Vaarsuvius of the Order of the Stick averts this to prevent a charging enemy from using his Mounted Combat Feats.

Video Games

 * In the jousting match in Defender of the Crown, subverting the trope by hitting the opponent's horse costs you the land you conquered.
 * Epona of The Legend of Zelda Ocarina of Time and Majora's Mask is completely invulnerable to harm, as is Link when he is riding her. Unfortunately Link can't take her everywhere he goes, stopping her from becoming a Game Breaker.
 * In Twilight Princess, Link is no longer invincible while riding Epona, due to a larger focus being placed on mounted combat. Epona herself is still invulnerable, however.
 * Epona's consistent invulnerability may be justified as she is implied to be some kind of divine spirit, based on her powerful bond with Link, reincarnation across several hundred years, and Meaningful Name. She may also be a reincarnation of Link's red loftwing in Skyward Sword, which is the same colour and also invulnerable in gameplay.
 * TP gives an even stranger example in the porcine mounts ridden by enemies, which actually can be attacked to a Non-Lethal KO, but from which they'll just keep getting back up after a while.
 * It is possible to charge them off a cliff or into a ravine, though.
 * The Legend of Zelda Four Swords Adventures uses horses for invincibility items.
 * Averted in Red Dead Redemption where you will likely lose a good many horses to gunmen, large falls, or vicious wildlife.
 * Averted in Shadow of the Colossus in which a stomp from one of the Colossi sends both you and your horse flying and you take damage. The horse will limp for a while and then stay out of the way until called again.
 * In many RPGs, like Ultima IV and Exile III, your horses are of no interest to enemies, and aren't even seen as creatures in the gameplay mechanics.
 * Dynasty Warriors and Samurai Warriors, where horses are just transportation when you are riding them, and just an immobile block when not rided.
 * Averted in The Elder Scrolls IV: Oblivion; horses can be fought and killed just like any other creature in Tamriel. They can even be killed whilst being ridden, and it's not uncommon to kill your horse while running down a too-steep incline if you aren't careful. The only (non modded) exception is Shadowmere, an invincible horse given to you for completing the Dark Brotherhood quests. Like every other invincible NPC in the game, she can still suffer a Non-Lethal KO.
 * Subverted to a degree in Mount & Blade. Horses can be knocked out, and if this happens there is also a chance they will be lamed. Being lamed temporarily lowers a horse's stats until it heals again (which can take weeks) but won't kill it unless it's already lame.
 * Sunset Riders: in the riding sections, the bullets just pass through the horses and only the riders can be hit. Except for stage boss "Dark Horse": a few bits of plating allow his horse to stop any bullets that hit it.
 * Completely averted as can be seen in gameplays of BioShock Infinite where a few dead or dying horses are visible in the aftermath of battles between the anarchic Vox Populi resistance faction and the xenophobic Founders on the floating city of 1912's Columbia. One notable scene has Elizabeth try to use her abilities to open a tear in the space-time continuum and heal a wounded horses with......varying results. In another scene, while fighting a Big Daddy expy called a Handyman, a panicked horse runs in the general direction of the Giant Mook who grabs it by the legs and flings it past Booker and Elizabeth like a base ball.