Mutants were Unique Creatures, that evolved in the Era following Blood Omen following the Collapse of the Pillars. They were orange or brown skinned and had a particularly unusual appearance; They had a relatively small body with two small atrophied 'legs', longer 'arms' with tridactyl claws (one of which was particularly large and deformed),long necks, and heads with a snout-like appearance and a central beak-like mouth.[Soul Reaver 2]
Ordinarily, mutants would walk on all fours, with their longer limbs dragging along the ground. In combat, they would stand up on the largest 'arm' (raising themselves to a considerable height) and attack with the other using a number of claw strikes. Mutants were a strong and tough enemy at close ranges, though they were slow, had poor defensive capabilities and attack range, and could be easily sidestepped.[Soul Reaver 2][Soul Reaver 2 manual][Soul Reaver 2 strategy guide (Prima)][1]
Mutants are referred to as "mutantba" in game files[Soul Reaver 2].
Though explicitly hunting Demons, the Demon hunter enemies will notably attack Mutants if confronted with them.[Soul Reaver 2][2]
In concept art mutants are notably depicted wearing armor to cover their bodies.[Soul Reaver 2]
Besides being described as 'evolving' era following Blood Omen,[Soul Reaver 2 manual] no further explanation has been given as to the origins of the mutants, and it is ultimately unclear what they were originally. The creatures could be considered tetrapods, with four discernible limbs, though only two of these (both 'arms' in the conventional sense) were used in any capacity in combat (with the two small 'legs' merely dangling usually).[Soul Reaver 2][2]
Mutants share the same skull-Soul as Demons and Thralls, perhaps suggesting they are not a 'natural' animals (which have the same yellow soul as humans), though they do appear to have Red Blood.[Soul Reaver 2][2]
Mutants at Dark Chronicle (by Ardeth Silvereni).
Soul Reaver 2
