The Rhyos, also known as the Jimera or Gorgimera, is an enemy in the original Final Fantasy. It is a Fire-based monster and often uses the Blaze attack on the entire party. Rhyos is found in the second floor of Temple of Chaos.
In the NES and Wonderswan versions, it has the ability Poison, which can potentially petrify the entire party, and which bypasses traditional protections like NulDeath and Protect Rings, making it especially dangerous, though it is stopped by Ribbons. It seems to have lost this attack in the remakes, thankfully, making it significantly less of a threat, though players of the earlier versions MUST be on their guard when facing this foe.
The Rhyos was originally known as the Gorgimera, and, like most monsters in Final Fantasy, is a Dungeons and Dragons reference. The Gorgimera was a form of Chimera that replaced the goat head with the head of a Gorgon, a beast which could breath poison that turned flesh to stone, hence its Poison attack in the original game.