From the campaign:
We are really excited about this one! So much so, that we are going to show you the photos that Fenris Games sent us of the Mutant. It is, technically, not finished or molded but you can certainly see how terrific this model is going to look.
The Mutant is one of the Monsters available to the Opener of the Way. His Cultists are actually able to "grow" into a Mutant, and then, later on, the Mutant can grow into an Abomination, and so up the line.