Mutants appeared in Soul Reaver 2. Raziel encountered them in the second time period, in the Termogent Forest Swamp, one hundred years after the events of Blood Omen.
According to the Soul Reaver 2 Game Manual (UK and US versions), the mutants 'evolved in the decades following Kain's fateful decision at the Pillars' - his decision not to sacrifice himself. This suggests they were native to the Material Realm, rather than being invaders from other realms (like the demons).
The mutants were a dark orange/brown colour and appeared to have four limbs: two short feeble legs attached to a small lower-body, and two arms, both ending in a three-clawed 'hand' (reminiscent of the Tentacles in Defiance or the tridactyl hands of evolved vampires). One arm was far larger than the other. Although it looked like they had eyes, their heads were almost featureless, except for their gaping mouths. Thin tendons or muscles stretched between their skull and jawbone.
While not alerted to Raziel's presence, the mutants appeared to walk slowly in a human-like way, using their tiny legs. Their arms seemed to support the weight of their hunched upper-body as they moved; the mutants pulled themselves forward with their smaller arm, and their larger arm was dragged behind.
When they noticed Raziel, the mutants changed their stance. They would lift their legs off the ground and 'walk' on their arms instead, allowing them to move much faster. When they wanted to attack, they would 'stand' on their larger arm, and swipe at Raziel with the clawed hand of their smaller arm.
The Demon Hunters in the Termogent Forest Swamp would fight the mutants if necessary, but Raziel would always be the first target of the Demon Hunters and the mutants if they noticed him.
We know that the mutants rapidly evolved into their Soul Reaver 2 form, but we don't know what they were originally. All we can observe is that they may have been humanoid (they had the right number of limbs), they had red blood, and their souls were inhuman (skull-shaped souls were released upon death, rather than the yellow ball-shaped souls characteristic of humans in that game).
- [SR2] Raziel: "This left me no course but to explore the era I now occupied, and see what changes this century had wrought following Kain's ill-fated decision."
- The Soul Reaver 2 Game Manual (UK and US versions)