Tretista Kelverian (トレテスタ・ケルベリアン, Toretesuta Keruberian?) is a boss in Mega Man Zero 3. Tretista is based on Cerberus, the three headed hellhound. He acts as the Chief Judge of the Eight Gentle Judges, and has three independent thought circuits that he uses to reach a fair judgement. These circuits act as the voices of compassion, agression, and reason. When Dr. Weil brainwashed him to be one of the Weil's Numbers, he could lost his ability to rationalize. Instead, his agressive traits were amplified, furthering his beast-like nature, and he became violent and brutal. During a mission, Zero went to investigate a giant elevator created by Neo Arcadia, and he finds Kelverian guarding it. Zero hence battled him and defeated the most powerful of the Eight Gentle Judges. Zero then discovers the elevator is used to transport massive amounts of E-Crystals to be used as energy.
Hounds of Hell: Tretista launches the dogs on his shoulder and they spring forth as guard dogs which jump around the battle field.
Death Tackle: Tretista hurls a huge crate onto the ground and then breaks it with a full-body tackle.
Judgment Ball: Tretista spits out numerous vaporous energy balls from his mouth and the other two dog heads. The balls will travel on the ground as well.
Bent Metal: Tretista holds a huge metal bar and then bends it with physical strength alone, before tossing it at Zero. The bar will bounce once after hitting the ground.
EX Skill Laser Claw : Tretista drops a huge crate onto the ground, but this time round instead of tackling it, he generates a purple energy laser blade extended from his claw and then obliterates the box with an impaling rush.