"Fishlegs can look past this Catastrophic Quaken's hard exterior, and see her softer side. He just has to look very, very hard."
―Dragons: Rise of Berk
Spikeback has a pudgy body that is deep purple in color. Unlike most Quakens that have brown or darker colors, Spikeback has glistening, crystal-like spikes that jut out of her back. She has several brown spots on her chin, wings and limbs.
There are giant spikes of crystals on Spikeback's stone slab in Dragons: Rise of Berk.