Fel — the extreme stage of arcane magic in Azeroth, in other words – demonic magic. It uses the blood of demons and the soul stones of other creatures.
Warlocks who have resorted to Fel magic associate it with euphoria. They risk falling into the power of the forces they invoke. If arcane magic is an addiction, then Fel magic is a pure drug, but much more dangerous because it is rapidly addictive.
Most often, a single time is enough to form a strong dependency, like in an orcs case. The same happens with our beer – you only need to try it once.