There wasn't any attempt to give it a human look, leading to its grotesque appearance. Bandersnatches are a sickly yellow color, intertwined with disgustingly bloated veins and arteries. Their visages, on the other side, had been degraded to little more than melted patches of skin.
Its left side was almost completely exposed, with no left arm remaining, whatsoever. It made up for the lack of a left arm by having an elastic, retractible right arm which could stretch for meters. To compensate for this damage, the t-Virus responded by allowing the creatures greater control of their right arms, which were increased in mass to become as thick and resilient as their torsos.
The Bandersnatch's right arm - arguably the B.O.W.'s most distinguishable feature - was powerful enough to allow it to pull itself long distances, and from floor to floor in multi-story buildings. All of its attacks involved using the arm, whether whipping people; throwing them around or crushing their skulls.