Basarios is a small, rocky wyvern that lives in Volcanic and Swamp regions. It is the juvenile form of Gravios. It is able to release either sleeping or poisonous gas from its underside, and on extremely rare occasions a fire plume. It is also known to unleash a very powerful lava beam at times. It can also hurl balls of fire like a Yian Kut-Ku, although it prefers to charge towards adversaries.
When resting or changing areas, it burrows underground, exposing only its back, giving it the appearance of a large grey rock. Being very heavy, it is a slow mover, and although it has wings, it rarely uses them to fly. Even when they do, their weight allows them only to fly for a short time. In Monster Hunter, they can only stay in one area. In the sequels, however, they have gained the ability to move to other areas.
Basarios charges in a manner similar to Diablos or Monoblos, although it is slower and cannot turn as sharply.
Despite Basarios' ability to hide, in most areas they are visible, since the rocks on his back are a slightly lighter color than other rocks.
In Monster Hunter Frontier Online, Season 9.0, a 'Hard Core' Basarios is introduced. This unique Basarios can now fire 3 heat-beams in rapid succession, followed by a burst of poison gas; it can roll-over to try to crush the hunter, and emit poison at the same time; it can dig and partly re-emerge to spew a powerful ball of fire; it can also leap at the Hunter. Its normal fire-ball attacks are now much improved, and it has what seems to be a branch in one of the rocks on its back.
- In the original Monster Hunter the Basarios stayed in only one area, Area 2 of the Old Volcano and Area 7 of the Old Swamp; it will never leave these two areas.
- Basarios takes 1.1x as much damage when underground.
- Basarios, along with Gravios, Bulldrome, Gigginox and its subspecies are the only monsters able to be flipped over on their backs when enough damage is done to either of their legs or by knocking them out with an impact weapon.
- When knocked out, just like Gravios Basarios will be flipped over on its back, where it will flail its wings helplessly, causing the wind effect.
- Basarios' tail is the smallest in the Monster Hunter world when cut.
- Basarios' chest can be broken once, and once this occurs the area becomes much more vulnerable to damage.
- Unlike the Gravios, Basarios has two horns.
- High Rank or G-Lvl Basarios (or one from a Nekoht Quest) uses a higher caliber poison than a regular Basarios, should its stomach be broken. This poison drains health twice as quickly as normal poison would. One can tell when Basarios is using this stronger poison; the cloud will be a darker purple and has poison bubbles in it.
- HC Basarios has some aesthetic differences, including poison stains on the rims of its pores and a branch growing out of its back. Their moveset and behavior appears to indicate they are nearing adulthood; new attacks include rolling on Hunters and releasing poison gas while rolling, jumping and body slamming, a triple heat-beam and releasing sleeping gas at any rank.