The U-3 displays the biological features of each of its genetic-benefactors, though imperfections in the technology that created it led it to appear asymmetrical in shape. The upper part of the body is that of a human torso, displaying a monstrously-warped face and marked by strange scars upon its nape and crown. Its spinal column is also human in origin.
The creature's right arm was clawed, while its left was a long tentacle which it used as a whip against enemies. Its four front and hind legs appeared bonded by a centipede-like fleshy piece of muscle.
After its initial defeat in a cage fight against Leon S. Kennedy, the creature mutated in order to continue hunting him. The Plaga residing in its spine erupted, giving it the ability to kill prey through the new set of jaws the parasite had to offer, being capable of slicing straight through a human being.
In its third form, the human-eqsque head seemed to "die", going limp and passive, while the monster used the Plaga head more and more exclusively, even using it to dig through the ground and ambush Leon from below.