In all the folklore of Anril, the Shapeshifters were usually depicted as the mount of Demons. They came to the human world in hellfire, along with blood and slaughter.
The birthplace of these beasts was definitely locations which suffered calamity. No matter if the disaster was natural or man-made, it was certainly a catastrophe that claimed the lives of thousands and millions. Only this could trigger the birth of the Shapeshifters, which were an amalgamation of pure negativity.
Suffering and hopelessness were the greatest sources of energy for them.
As they were created from negative emotions, their bodies were neither tangible nor a figment, and were born with all sorts of Dark Magic. At birth, they would be at least level-16. When they had finished evolving, they might surpass the level-20 mark, and become a Legendary Beast.