Demons

Demons are commonly observed escaping from various portals into Mundus, sometimes by accident and sometimes through pact magic, the occult art that uses human skulls in exchange for power. One of the most famous of these beings is Tenamuach, known to some as the Great Devourer. It was difficult for me to find more information on these beings and their nature. Followers of the religion Tératos and those that follow the occult art of skull magic might have additional information or theories.

I am not sure about the relationship between demons and other planer entities.