Originally posted by Reaver79:

Not even as a pay for skin, this is so lazy..

There's isn't 100% coverage, and not all of them are always on sale due to the current shop implementation, but there are several mutations as paid cosmetics. The Underworld Denizens team bundle includes tentacles cosmetic for Goblins, and about four "Claw" variants (each of those four fully replaces the right arm with something else stabby or scratchy).

cyanide have said that there not adding visible mutations to the game
but who knows with the new publisher if it will change in future

This came up when BB3 released. Cyanide said it was a GW decision that all models had to match the tabletop versions with no differences.