The Reptilicus are the native dominant race of the planet Bryyo in Metroid Prime 3: Corruption. Once an advanced and enlightened race known as Bryyonians, they descended into primal savagery following decades of conflict between the Lords of Science who favoured scientific advancement, and the Primals who rejected technology in all its forms. The war between the two factions left much of their planet a ravaged wasteland and only the Primals managed to survive in the end due to their greater numbers. Over time, they became ever more savage and warlike, and after a Leviathan Seed impacted Bryyo and contaminated the planet with Phazon, the Bryyonian remnants eventually de-evolved into the Reptilicus creatures that Samus Aran would one day encounter.
A Reptilicus can be distinguished from a Reptilicus Hunter by its generally darker coloring, as well as the spiny protrusions located on its back, similar in appearance to the flora on Bryyo. They are large, lizard-like creatures with six limbs, standing on their back two legs when wishing to attack and for intimidation. They appear to wear a skull-like mask on their faces.
They use highly advanced technology despite their feral appearance; they have the ability to teleport and use high-tech weapons, including an electrical whip-like weapon, some form of boomerang and a projectile weapon, possibly arcane. They are resistant to Fuel Gel but weak to extreme cold, so it is possible that they originate from one of the warmer regions of the planet. Likely because of their strong affinity with Fuel Gel, they are immune to the burning effect of the Plasma Beam, but can still be killed if they fall into Fuel Gel. Reptilicus also use Warp Hounds for assistance, creatures that have been trained to ambush enemies, and that share the teleporting ability of the Reptilicus. Warp Hounds are most often used by Reptilicus Hunters over the standard Reptilicus, showing that the Hounds are used for hunting purposes as well as guarding.