To say Sigil Fernel was cruel was putting things mildly. As a boy he probably enjoyed tearing the wings off of flies and replacing them with parts from other insects, all before attempting to bring them back to life. This early trait translated well into his adult life.
Sigil possessed considerable necromantic skill and probably a degree of surgical prowess as well.
Nothing pleased Sigil more than constructing his own horrifying reanimated creations from the body parts of many creatures.