Re: Certain gods in real-world pantheons
I'm not sure the concept works. On the whole, there really isn't a god of evil in most real-world pantheons. Instead, evil is usually attributed to "those other guy's gods" or "the gods that our gods displaced to make the world a perfect place for us".
For the Greeks, the Titans were evil.
For the Norse, the Giants (and a few others) were evil.
Egypt. This one is kind of funny. Set became the god of evil after the unification of Egypt (during the reign of Narmer) because the religion of Set fell into disfavor with the state religion (probably due to a failed rebellion followed by the typical "history is written by the victors" thing). Prior to Set, the "evil" deity for them would have been Apep (or Apophis), the Destroyer - but he's really more a figure of folklore and was never actually worshiped. (It's interesting to note that Set's original role was to battle Apep and keep him from destroying the Sun Boat of Ra.)