Altrymis is a big monster that resembles a Gastornis, with a strong axe-like beak and armored, muscular hind legs to run. Altrymis' body is bulky and covered with a soft coat of feathers, its back is quite smooth and the tail isn't noticeable. Its front legs are small and weak and it has a feather crest on the head.
Altrymis has a brutal demeanor and inflicts heavy damage to its foes, boldly attacking hunters, scaring off other large monsters and even stealing food from them. It's a prideful, vicious beast, but under all its bluster Altrymis is just a big chicken.
Altrymis mainly attacks with strong bites or slashing its beak like an axe, it can also charge at great speed or kick with its muscular legs. Like the Galetrice, it can be startled by sonic bombs, and it will quickly panic and run away if another monster decides to confront it instead of fleeing. Targeting its legs or attacking it while over a ledge can make it topple onto its back, where it panics and rocks around helplessly like a turtle before eventually righting itself. After suffering such indignities it usually goes into rage, where it can cause quake with its feet and spit slimeballs that paralyze hunters.
- Its head, back and hind legs can be damaged.