In my "Mutants in the Now" game, the GM has established a Magic System in the world where characters can obtain Dark Powers, but only once they have sacrificed something personal and important to themselves; The bigger the sacrafice, the greater the power.
Drac for example was willing to sacrafice his ties to humanity after becoming a Vampire Bat Mutant so he wouldn't feel bad about killing humans, he can just think of them as a resource, and in turn he becomes more powerful, but he still has a familiar connection to other Mutants and his gang, the Amata-Ryu. Dark Magic is one hell of a power trip though, and once you cross one line it makes it a lot easier to start crossing all of the lines.

Omen is what you get when you sacrafice everything for power. Externally he appears to be a Xoloitzcuintli or "Mexican Hairless Dog"; They get their names from Xolotl the Aztec Dog God who is the Guide to the Underworld and among other things is the God of the Diseased, the Deformed, and Monsters. While in Aztec myth, the god Xolotl is a good omen, there is nothing good about THIS Omen, infact, there is nothing left of who he used to be at all.
He has become an apathetic moral black hole who's given his entire soul for Dark Magic. For all intensive purposes he is a literal Demon, there is no line he will not cross, he doesn't even comprehend the feeling of pleasure for being entirely morally bankrupt, he simply exists as a being of absolute evil.

He's 10 feet tall mutant of an unknown origin. Due to his elusive nature a fog of urban legends and rumors clouds the much darker motives. According to The Witch she once met a devilish man, a man who only knew of violence and depravity seeking to torture the life he disdains. Learning of magic and rituals by sacrificing portions of one soul the witch heard from a confidant that an entire village in Mexico was slaughtered and sacrificed. Every man woman children animal and monster (mutant) could only be described as nightmarish. Omen quickly rose in the criminal underworld as almost a boogeyman with committing crimes even the cartel may reconsider. His most infamous rings are his mutation drugs ring and the "House of Bats" black market. Acquiring large amounts of raw unrefined goo from back door deals from Gen Corp or other providers he makes drugs and weapons to cause and spread unstable mutations. The mutations have a known 65% survival chance but the mutations are wildly unpredictable. The mode insidious incidents is where he disguises the drugs as candy and stickers and sells them to the general public.

The house of bats is its own horror story, Omen views all life as 2 things pawns and food, and the pawns need to eat. His black market has all illegal cuisine imaginable. Doesn't matter if the animal is endangered, genetically modified, or even fully sentient food is food. The big ticket items....fresh mutant meat. If you ever get an invite to the house of bats there's an equal chance you would be the entree served. Humans aren't safe either as they can end up in the market as a customer or as a product. Omen is the closest someone will get to meeting the devil himself. But you are most likely to see his court of officers who live up to their own legends