Firstly, a few extra details gleaned from the source material
Head described as "dome-like", also features visor-like lips over knife-like teeth and some kind of jaw mechanism.
Now for the "Diegesic analysis" (assuming my translation of the brief is correct).
The world is fairly standard western-european fantasy, with a technology level equivilent to medieval europe. The killing machines are the product of two in-world cultures - they are designed by someone from a central-european-style culture, but produced in a northern-european-style culture.
Based upon the descriptions, its hard to tell whether "killing machines" are principally humanoid or more based upon animals, so the next step will be to experiment with some silhouettes.