All of Bristleback's default items except for the back item are missing backfaces. His default head spikes are invisible when viewed from behind, his eye patch is transparent from behind and his bracers, the green patches on them disappear as well.

As for his model, his mouth has a giant hole in hit, visible a bit when he talks, but very visible when using Viscous Nasal Goo. And his belt thingy (which cannot be customized), his apron is inivisible when viewed from behind, and the green things on the sides are as well.