- Order: Saurischia
- Suborder: Theropoda
- Superfamily: Forefoot Fist Wyvern
- Family: Brachy
Brachydios is a member of the Brute Wyvern classification. It is unique in this class because it has highly developed forearms, unlike the nearly useless forearms of most other Brute Wyverns. Some Brachydios individuals venture into special environments to become the giant Raging Brachydios.
The known habitats of the Brachydios in the New World are the New World Volcano, Deserted Island, and Tundra. In the Old World, they are found in the Volcanic Hollow, Volcano, Frozen Seaway, Polar Sea, Snowy Mountains, and the Everwood.
Brachydios is an apex predator, that has been shown to be able to defeat other large predatory monsters like Agnaktor. Brachydios competes with Agnaktor, Rathalos, Brute Tigrex, Tetsucabra, Teostra, Seregios, Glavenus, and Deviljho. With the unique slime mold at its disposal and its extreme aggression towards intruding monsters and hunters, it would be more than a match for most other predators. Brachydios will occasionally feed on ore. Elder Dragons like Alatreon, Crimson Fatalis and Dire Miralis, along with the Flying Wyverns, Akantor and Ukanlos, could be a huge threat to Brachydios.
The symbiotic slime-mold is easily one of the most unique and defining feature of the Brachydios. The theropod's armored shell is hardened to protect against the explosive blasts that the mold creates on impact. A Brachydios's skin is similar to that of a thermos flask, giving it the ability to withstand both extreme heat and cold. Brachydios's body is the only place this mold can survive without turning explosive. When attacking, Brachydios constantly scrapes copious amounts of this mold off of its body, causing it to deplete. However, it seems that the beast's saliva acts as a powerful stimulant, which causes the mold to almost instantly replenish itself. The mold seems to have chemical reaction when enraged, as even areas of this Brute Wyvern's body with a very fine and otherwise invisible coating of it flare up bright yellow. In this state, the mold becomes far more volatile and explodes when it impacts virtually anything. The method in which this slime mold congregates on young Brachydios has not yet been determined, but it is generally believed that its explosions release countless spores that are sent long distances due to the blast. These blasts, combined with the very wide range of habitats in which the Brachydios is found, allows this mold to spread over great distances. Some scholars even believe that the mold may be able to grow in other environments, but that the shell of the Brachydios is the catalyst that makes it volatile. This theory has yet to be proven. In the Val Harbor region, Brachydios have learned to use their horns to make a massive slime puddle that can kill prey and any other monster that doesn't have protection against it.
Usually, the slime mold is living in harmony with Brachydios. Both spreading spores and exploding at the same time but the slime mold remains dormant on a surface even after exploding. If something like crustal movement or eruptions happens than the long dormant slime mold becomes active again. This long dormant slime mold has accumulated power while being dormant and has massive explosive power. This special slime mold is used for sex appeal, showing off a Brachydios's strength. This slime mold is the reason why some Brachydios go to or visit the Ingle Isle. Powerful individuals that gain this new powerful explosive slime become Raging Brachydios and this slime mold seems to be related to the reason why those Brachydios get so big.
Brachydios are extremely aggressive creatures and will not hesitate to attack if they feel threatened or challenged. Due to their aggression they are commonly known to invade the territories of other large predators, usurp them, and claim the territory as their own. They will also show no mercy to small monsters, like Uroktor who are seen in the Brute Wyvern's territories. Young Brachydios will live near their parents and their territory, yet the adults will not show any parental care at all. The young will pick up slime mold left behind by adults. However, this can be dangerous as their hides are underdeveloped and can possibly be seriously injured or even killed by the explosions of the slime mold. The Slime Mold on each Brachydios is different from the other and larger Brachydios are known to go on rampages from this mold constantly breeding for them.