| "'Feejee Mermaid' has become the generic term for the many fake mermaids that can be found around the world..."
This article contains information relating to a hoax. According to Cambridge dictionary a hoax is "a plan to deceive a large group of people; a trick."
The creature was described a shapeshifter to some degree. It could turn itself into a human form and its demon form, and was possibly fully sentient. It could however be distinguished from other humans by the fact that it smelled like sulfur and possessed hooves even in its human disguise. The creature would then ask random person for an hour, and after the person would respond the demon would kill him or her, or some other person on the rave party and then mysteriously disappear.
From a political point of view, much like Poland's other demonic cryptid Black Volga, the Disco Demon probably was made as a hoax to scare people into not going to rave parties. The same thing applies to the Sataniści.