Two-Back has the appearance of a mutilated humanoid with its lower front fused into the lower back of a large monstrous creature. The appearance suggests the two mutilated creatures are participating in a sexual act, as the top figure's hips are against where the bottom figure's anogenital region would be, and when idle will thrust forward intensely against the bottom figure while flicking its tongue.
The larger humanoid's front arms are stubs that end in horrific needle-like protrusions, while the smaller/"back" humanoid has stubs as both its arms and legs, also having needle-like limbs. They are both made of flesh covered in blood. The figures are connected by a stretched piece of skin between them. The bottom figure is hunched over with its head hanging down. The top figure is on its stomach with an arched back and its head falling back.
Two-Backs will attack by spewing acid, or ramming into Travis Grady. They may also lunge at him and pin him down, which is quite damaging, as they drive their needle-like protrusions into his chest and spew acid on Travis's face as they do this.
The Two-Back represents Travis's inability to have normal relationships and likely sexual deprivation as a lone trucker. In an early cutscene, a fellow trucker mentions that he should find himself a nice girl. In the Bad Ending, it is hinted that Travis was a serial killer that targeted females. They appear frequently at the motel, and some motels have a reputation for being sex sites. In one room, Lisa Garland and Michael Kaufmann are seen buttoning up beside a heart-shaped bed.
Among the other Shakespeare references in the game, Othello is also referenced. In the play, Iago describes Desdemona's sexual relationship with Othello by stating that they are "making the beast with two backs". This is a reference to intercourse, supposedly fusing two people into a single beast, in this case, literally.
- The namesake of "Acid Horse", a song in Origins' soundtrack, may be an allusion to the Two-Back, given the lower figure is rode as such, and can attack through emisis of a lethal gastric fluid.