Brachydios is easily identifiable by its glowing, green slime-covered horn and "fists," as well as its shiny, armored hide covered in many plates and ridges made of obsidian. Unlike other Brute Wyverns, Brachydios sports a pair of long, highly developed forelimbs that it uses as its primary means of defense. Despite initial appearances, Brachydios does possess claws on its forearms that are tucked away underneath, and serve no apparent purpose in battle.
The forelimbs and horn of Brachydios are covered in a mysterious, green slime. By slamming the ground or prey with its fists or horn, Brachydios can deposit a puddle of its slime mold, which, once detached from the monster's body, quickly undergoes a powerful chemical reaction and violently explodes. This slime will gradually run out, in which Brachydios can "prime" this mucus with its saliva to replenish the it. The substance itself is also sticky; if a hunter is struck directly by one of the monster's fist or horn attacks, it will adhere to the hunter's body and eventually explode. Hunters can remove the substance by rolling or using a Deodorant. Notably, Brachydios is also capable of leaping far distances by using its powerful hind legs and is much more agile than other Brute Wyverns.
When enraged, various parts of Brachydios, such as the fists, horn, and various ridges along is body glow a bright yellow and orange. In this state, attacks that would leave a slime puddle will instantly explode upon impact instead.