The Deviljho is a chaotic beast noted for its high level of aggression even among Monsters. An apex predator, it will kill and attack anything it can, up to humans, other Monsters, and even its own kind, regardless of the risk. The creature has even been known to eat its own tail if it is severed. They are classified by the numerous scars they have received in doing so, and are extremely hard to kill even by the blade of an experienced Hunter. The Deviljho constantly wanders, eating whatever it can due to its high metabolism, never full and always hunting. A formidable predator, no Hunter is encouraged to engage a Deviljho in combat, and the only way to safely deal with one is with an entire team of veteran Hunters. Despite the enormous risk, this has not deterred mankind from capturing Deviljho and pitting Hunters up against them in arenas throughout the New World. The Deviljho is able to attack based on its environment; the rocks it hurls will correspond to the area it is fought in and inflict a Blight accordingly.
The Deviljho's "rage mode" is also highly notable. If enraged, the Deviljho's muscles will swell up, revealing its numerous scars, and it will start bristling from a unique energy from its mouth. It can spew this energy in the form of a beam, which will result in terminal damage to whomever it hits and causes Dragonblight to humans caught in the path. If enraged, a Deviljho will chase down whatever it sees until it has been killed or is out of range.
The Deviljho appears as a creature similar to the Tyrannosaurus Rex. It is a large creature, roughly as long as a bus, with a spikey tail as long as its body, massive feet and claws, a spiked chin, and a fearsome, enormous maw. It constantly slobbers, and its saliva, while caustic, is actually considered precious. It has a pale green coloration, and is adorned by spikes and scars all over its body. If sent into rage mode, its muscles swell up, the scars become more visible, and it glows red, as does its eyes.
The Deviljho was originally only able to have been fought online on the servers of Monster Hunter 3. However, on High-Rank, the Deviljho first appears ambushing and killing a Great Jaggi on an early High-Rank mission. From there, the player encounters the Deviljho numerous times. Whether this is the same Deviljho or not is unspecified, unlike in the case of the Lagiacrus. Near the end of the High-Rank quests, the Deviljho's quest is unlocked, and the playable Hunter can confront and ultimately capture or kill the beast. The Deviljho's parts are considered highly valuable. Numerous, equally aggressive Deviljho appear throughout the game.