How would a GM go about upgrading a monster and its Challenge Rating? Say a mad necromancer dips a skeleton in some sort of liquid metal that makes them stronger and harder to break. And or gives the skeleton a magic weapon such as a vorpal blade or a +3 weapon or armor. I did say he was MAD right?
How do you go about calculating the new CR for this creature?
Also are there any examples of necrotechnology in Pathfinder or D&D modules?