153 himself dug him out of the bio-waste disposal area, and reactivated him. His appearance is like that of a dragon, and appears to be a highly mutated reptilian creature clad in cybernetic armor, as evidenced by the gaps in the armor showing warped flesh.
He possesses a powerful laser cannon in the back of his mouth and razor-sharp claws which he uses to attack at close range. It is also remarked by 153 that his temperment control circuits are malfunctioning, leading to his aggressive behavior. Upon beating him, the Desert Eagle is unlocked for use in repeat playthroughs.
In the beginning of Thing-Thing 4, the corpse of Vahl Drieg is seen in the intro cutscene. Project 154 uses his energy core as a bomb to break out of the containment chamber.