Bridles are key items from The Legend of Zelda: Breath of the Wild. Link can purchase the default Stable Bridle from stables upon registration, and equip them onto wild horses that he tames, along with saddles. Bridles have reigns allowing Link to control the horse more humanly, as he holds onto their mane to control unregistered bridleless horses when riding bareback.
Link can obtain other bridles as rewards in mini-games. The Traveler's Bridle can be obtained by using the amiibo Rune with the Link Rider amiibo of the Breath of the Wild series, though it is worn by Link's unnamed horse from a century prior which appears in three Recovered Memories cutscenes indicating Link owned one before the Great Calamity. The Monster Bridle can be purchased at the Fang and Bone using the shop's special Mon currency which can be obtained by sell monster parts to the owner Kilton. Link can change bridles at certain stables by talking to a female stable hand. However he must have fully bonded with a registered horse in order to change its bridle and must have obtained a different bridle from the initial set first.
However some horses such as the Giant Horse from the side quest "Hunt for the Giant Horse" or Epona, obtainable through the amiibo Rune, are equipped with special bridles upon registration that is unique to them and cannot be changed. However the stable hand will state that Epona will not like it. In the case of the Giant Horse, his size prevents Link from changing bridles as only its default one fits. However the White Horse can be equipped with any bridle or saddle though it receives the Royal Bridle from Toffa after taming and registering it as part of "The Royal White Stallion" side quest along with the Royal Saddle. The Extravagant Bridle and Knight's Bridle are prizes received in Horse related mini-games.
Unlike armor worn by Link, bridles are purely cosmetic, and do not affect a horse's stats or increase their defense. The sole exception is the Ancient Bridle ("The Champions' Ballad" DLC), which increases a horse's stamina meter by two spurs. (It is also claimed that the Knight's Bridle reduces damage, but this requires testing.)
Horses are automatically equipped with their default bridle upon registration, though once Link has acquired a bridle key item he can speak to one of four female stable hands: Breen (Woodland Stable, Canni (Outskirt Stable), Phanna (Highland Stable), and Tenne (South Akkala Stable) to change bridles once fully bonded with said horse. Epona and the Giant Horse's unique bridles cannot be changed. Stable hands refuse to change Epona's due to her being fussy about her appearance, while the Giant Horse's bridle is larger custom made bridle designed to fit it as other bridles are too small and the stablehands are wary of its wild temperament and large size which make handling it difficult.
The default Stable Bride only appears in the bridle menu when changing Bridles and is absent from the key item menu as they are always purchased upon registration of any horse, besides Epona and the Giant Horse. The White Horse receives a Stable Bridle upon registration, though Toffa will replace its currently equipped bridle with the Royal Bridle as a quest reward for Link taming and registering it. However the Royal Bridle is a Key Item so it can be equipped to other horses after being acquired in "The Royal White Stallion". Besides the Stable and Royal Bridles, the White Horse must be fully bonded for stable hands to change their equipment as Toffa equips the Royal Bridle only once as part of the side quest regardless of the White Horse's bond with Link. Any horse equipped with the Stable set upon registration can have its equipment and mane changed by said stable hands once fully bonded. Once equipped a bridle will automatically be equipped to a horse when retrieving it from a stable. Since only one registered horse can be taken out at a time, the same Bridle can be equipped to multiple horses without issue as the bridle will be removed when said horse is board and automatically equipped to the horse being taken out. Link's Bridle Key Items always remain in his Key Item inventory after being acquired even during "Stranded on Eventide" and Trial of the Sword. They also remain in said inventory even when physically equipped to a horse. Epona and the Giant Horse's unique bridles lack menu icons as they are default bridles that cannot be unequiped similar to the boxers Link wears as a undergarment.
Link can bond with horses by soothing them after they follow commands though this method is a slow and tedious process. The quickest method is to feed them food such as Apples and Swift Carrots which horses will eat off the ground or out of Link's hands if he is holding it. Once horses stop eating they will be fully bonded with Link and become obedient. Horses can become bonded fully before or after registration, though again they must be registered and fitted with the Stable set to equip horse gear. Epona and Bokoblin tamed wild horses are automatically fully bonded though Bokoblin tamed horses are the only ones Link can change bridles with after registration though they generally have low or basic stats compared to wild horses caught and tamed by Link himself. The Ancient Bridle is the only bridle confirmed to effect a horses stats when equipped, thus save for it equipping other bridles is generally a optional cosmetic change.
List of bridles