It's a dynamic system where skulls imbue monsters with various stats, adding an element of unpredictability to encounters. There are four types of skulls: white, orange, red, and black, each bestowing distinct enhancements upon the creatures they adorn.
You can find some monsters with white skullls and they got some stats:
You can find some monsters with orange skullls and they got some stats:
You can find some monsters with red skullls and they got some stats:
Black skulls assigned only to the bosses, so every monster with a black skull is a boss.