Source: http://monsterhunter.wikia.com/wiki/Brachydios

Brachydios is a Brute Wyvern introduced in Monster Hunter 3 Ultimate.

Brachydios are easily identifiable by their glowing, green slime-covered horns and "fists," as well as their shiny, armored hide covered in many plates and ridges that are 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. Brachydios' forelimbs and horn seem to secrete a mysterious slime. According to in-game information, Brachydios "primes" this mucus to explode with its saliva, hence why it licks its arms, making it appear brighter green. Despite initial appearances, Brachydios does possess claws on its forearms that are tucked away underneath, and serve no apparent purpose in battle.

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. The substance itself is also sticky; if a hunter is struck directly by one of Brachydios' 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, Brachydios' fists, horn, and various ridges along is body glow a bright yellow and orange. In this state, Brachydios will no longer leave slime puddles, but will instead cause explosions directly on impact with almost all of its horn and fist attacks.

Brachydios' name comes from the latin name for arm, brachium (ブラキウム). This was used to make a reference to Brachydios' shell, which is made of obsidian (オブシディアン).