Dragons are a highly-intelligent but mostly nomadic species of large, winged, serpent-like sentient creatures. They range significantly in size, and can be anywhere from a foot at youth to several dozen meters in late adulthood. Their bodies are covered in scales, which can be a wide variety of possible colors. Unlike most mortal creatures, dragons can have lifespans lasting centuries.
Prior to the Great War, dragons had no real alignment nor organized society, and most merely roamed around the land in search of places to reside and store their hoards, only occasionally being spotted within the borders of the pony nation of Equestria. During the Great War, many dragons were persuaded to fight for the zebra empire against Equestria.
Before the war
Dragons are mostly solitary creatures that make their homes in caves, away from population centers. They collect their own treasure hoards that mostly consist of gold and gems, though this can also include items like books, such as Spike's own hoard which had a vast collection of unedited, pre-war literature.
Celestia had an arrangement with a female dragon, allowing her to guard the Canterlot treasure vaults in return for her dragon eggs which were to be hatched as part of the entrance exam for Celestia's school for gifted unicorns. This dragon was also the mother of Spike, though she had no contact with him until long after the great war. Twilight hatched Spike from one of these eggs and she was allowed to help raise him, in return he worked as Twilight's assistant during her youth and young adulthood, often viewing Twilight as his mother; even 200 years after the war and even after meeting the Dragon from Canterlot at long last.
Two other dragons were found to be living close to Ponyville before the war, the first was a large red dragon that made its home atop a mountain. The red dragon was settling down for a centuries long sleep but his snoring was creating smoke clouds that would cause massive ecological damage. The red dragon was convinced to leave by Twilight and her friends, specifically Fluttershy who gave the dragon a harsh lecture.
Another dragon was a teal/green dragon that was living in a cave, inside Everfree Forest. The dragon was aggressive as it found the baby Spike, stealing from its treasure hoard. Twilight Sparkle and her pet owl, Owlicious managed to rescue Spike and escape the rampaging dragon.
During the war
Many dragons fought in the war. Most notorious were dragon mercenaries the zebra persuaded to fight for them. Equestria responded by developing weapons, specifically built to kill dragon, such weapons were used on various types of cloudship: the Raptor-Class Cloudships earned the nickname of "Dragon Killer", due to their reputation in fighting Dragons head-on with successful results. Dragon eggs were also used by the Zebras to create Balefire eggs, a type of explosive ammunition that is launched from the Balefire Egg Launcher, B.E.L.
After the war
Many dragons that weren't killed outright by the balefire fallout of the apocalypse, survived in their cave homes unchanged or became ghouls, like the group of adolescent ghoul dragons in Canterlot or their broodmother "Mouse". Some dragons were born more recently, like Mister Topaz, suggesting there are still enough dragons unaffected to continue procreation.
Notable Dragons in Fallout: Equestria
- Mister Topaz: Leader of the Raiders, living in Shattered Hoof Re-educational Facility
- Spike: Currently living above the cloudline in a Cave, on of the few surviving characters from before the war, serves Equestria under the alias of Watcher and as the guardian of the Gardens of Equestria.
- Cyberdragon: An ancient Dragon that is far older than Spike or Mr.Topaz. He was found living in Everfree Forest by Red Eye, in a very sorry state. The Dragon was so old, he couldn't move under his own power, however he still had powerful fiery breath. Red Eye gave the Dragon Cybernetic implants to help it move again and the dragon in turn served Red Eye.
- Mouse: Spike's mother, a dragon that provided the eggs which Celestia used for the entrance exams for her school of gifted unicorns. After the War, she became saturated with the Pink Cloud that surrounds Canterlot that she's effectively became its source. She was turned into a mouse by a spell created by Nightseer's group of Alicorns in an attempt to clear out the Pink Cloud that was activated by Littlepip. She survived the destruction of Canterlot during Operation Cauterize.
- Adolescent Ghoul Dragons: A group of dragon ghouls that Littlepip and her friends encountered during their trip to Canterlot. Velvet Remedy negotiated access to Canterlot by giving them a gem covered dress to eat
Dragons in Side stories
- A group of Feral Dragon ghouls were living near a town, in an abandoned cave network. Blackjack, P-21 and Morning Glory cleared out the caverns and managed to kill all the Ghoul dragons for a job.
- The Thunderhead Enclave, allegedly killed a massive black dragon, the kill was made by Morning Glory's father Sky Striker who met Glory's mother, Dawn, during the operation. Dawn's version of the story claimed the dragon managed to escape.
- Precious is a pony-dragon hybrid that was created through Project Chimera.
- Rango: A young, orange scaled dragon that was being pursued by the Mite-y gang.
- An ice breathing dragon named Hyperion, lived near the summit of the Chimmerchill mountains, alongside his mate. Hyperion's ice breath had the power to magically preserve anything encased within the ice, the ice melted when Hyperion was killed.
- Hyperion's mate. An unnamed female dragoness, the mate of Hyperion. He preserved her in ice in a desperate attempt to save her from a fatal wound. She was later killed, at her own request due to the amount of pain she was suffering and the length of time it would take her to die.
- Andromeda. She was hatched from an egg that formed from the remains of Hyperion. Andromeda is an azure blue dragoness, who Mach chooses to raise, seeing her as a personal responsibility.
- The pony Dragonslayer, claimed to have killed a dragon that he lured into a trap.
- A feral dragon appeared in chapter 7, and is most notable for killing Mud Swirl, Stitches adopted brother, to save Zoey. It is killed by the Angel Hunter's later on in the chapter, saving Dead Hooves life as well as breaking the unfortunate news the Mud Swirl had died to Stitches.
Dragons are omnivores and lithovores, capable of eating a wide range of meat, vegetables/fruit and gemstones such as turquoise, emeralds, rubies and diamonds. They can grow to be truly massive and live to be centuries, possible millenia old. Dragons are capable fliers and have notoriously strong scales, they can also breath fire as a form of attack. Dragons are also susceptible to ghoulification.
Revealed in S02E10: Dragons begin to grow in size as they collect or hoard things, be it gems or simply useless junk. This may not be true of all dragons, but it at minimum applies to Spike. It is possible that dragons can grow based on the value and not the quantity of their possessions, making Spike the great-granddaddy of dragons since he has the most important treasure in Equestria. The growth is based somewhat on perceived ownership, as Spike returns to normal size once he relinquishes everything he has pilfered.
It would then be possible for keepers of dragons to artificially empower their pets by granting them a wealth of gems, treasures, or perhaps even influence/power in the form of slaves. Unknown if offspring qualify as possessions, which would have made Spike's mother a behemoth.
Spike also mentions in this episode "growing" his fire ruby for his own birthday.