Large, darkly colored mountain lions with bony, horn-like protrusions on the face and down the spine. Some individuals claim to see a flame like energy engulfing them. Thankfully they are relatively rare (but not unheard of) in this age due to hunting by wardens and trappers.
The origins of hellcats are unknown. Some say they were weapons created by the gods during the War of Essence to hunt down magic users. Others say they were an experiment gone wrong of a wizard dabbling in forbidden arts. Most believe them to be ordinary beasts. Then there are a few who actually believe the cats to have literally come from hell.
What is generally agreed upon is that hellcats turn up where people are tampering with things they ought not be tampering with. They seem to be drawn to people with relics and texts from ages gone by.