Greater Mutants are creatures unique to the game.
While ingenuity and technique have their advantages, sometimes a sweeping blow with a huge club is the best solution in combat. That is why Salamandra created greater mutants. After all, someone (or something) has to wield that huge club.
"The Greater Mutant has proved to be disappointing. It turned out to be a beastly mutant with superhuman strength, terrifying cruelty and scarce intelligence.
Fortunately, our masters were satisfied. The Greater Mutant has its place in their plans. I even think that our masters' plan is mainly based on using such creatures."
Developer CD Projekt's characterization of the Greater Mutant taken from the monsterbook, which was enclosed with the Collectors Edition of the computer game The Witcher for Poland, Hungary and the Czech Republic:
These huge creatures are humans who were exposed to the process of mutation. This violent transformation stripped them of all humanity and transformed them into strong, aggressive beasts possessed by destructive rage.
The author of the concept drawings captured the greater mutant's main features: its imposing, barbarian stature and the monstrous facial expression and bodily deformations deriving from the transformation. The artist emphasized the beast's mass and muscularity by stripping it of its skin, as shown in the colored illustration. The bony, protruding spikes indicate that its skeleton was also strengthened. Rendering the mutant similar to some sort of archaic monster, they also suggest the transformation was extremely painful.
| " 'I was present when they did the autopsy on one of them,' said the wizard. 'Geralt, what we found inside the skull and marrow could not be described. Some sort of red sponge. The internal organs were all mixed up, some were missing completely. Everything was covered in moving cilia, bluish-pink shreds. The heart was six-chambered, with two chambers practically atrophied. What do you say to that?'
'I've seen people with eagles' talons instead of hands, people with a wolf's fangs. People with additional joints, additional organs and additional senses. All of which were the effects of your messing about with magic.'
'You've seen all sorts of mutations, you say.' The magician raised his head. 'And how many of them have you slaughtered for money, in keeping with your witcher's calling? Well?' "
— page 84, The Last Wish (UK edition)