Basarios are small, rocky Flying Wyverns. They are the juvenile form of Gravios. Their hard, stone-like shell can be used for protection against other large wyverns, doubling up as effective camouflage when Basarios partially bury themselves in the ground.
They are able to release either sleeping or poisonous gas from their underside and, on extremely rare occasions, a fire plume. They are also known to unleash a very powerful lava beam at times. They can also hurl balls of fire like a Yian Kut-Ku, although they prefer to charge towards adversaries.
When resting or changing areas, they burrow underground, exposing only their back, giving them the appearance of a large gray rock. Being very heavy, they are slow movers, and although they have wings, they rarely use them to fly. Even when they do, their weight allows them to fly only for a short time. In Monster Hunter, they can stay in only one area. In the sequels, however, they have gained the ability to move to other areas.
Despite their ability to hide, in most areas they are visible. This is because the rocks on their back are a slightly lighter color than other rocks.
Basarios charge in a manner similar to Diablos or Monoblos, although they are slower and cannot turn as sharply. They are less aggressive than their adult counterpart form, Gravios.
In Monster Hunter Frontier Online Season 9.0, a 'Hard Core' Basarios is introduced. They have a branch in one of the rocks on their back, bright blue eyes and purple stains around their stomach pores.
These unique Basarios can now fire 3 heat-beams in rapid succession, followed by a burst of poison gas; they can roll-over to try to crush the hunter, and emit poison at the same time; theycan dig and partly re-emerge to spew a powerful ball of fire; they can also leap at the Hunter. Their normal fire-ball attacks are also now much improved.
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.
The Basarios stays in only one area, Area 2 of the Old Volcano and Area 7 of the Old Swamp; it will never leave these two areas.
High Rank or G-Lvl Basarios 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 contain poison bubbles within it.