ActRaiserTheReturned said
Well, basically, I"m looking for a recovered Earth planet that developed magical powers centuries ago, and is currently in the Space Opera age. It has psionic powers like telepaths and telekinetics, wizards, and the mystical kinds of psionics like Force Users. Of course, it also went through a mythical age with people like Pagan gods as well as a supreme, more 'Godlike" deity, having angels as servants. Although, to be fair, Lucifer is definitely powerful enough to be an Elder god even in Mortal Kombat. The fights we see on the show are just because they need avatars to function on Earth. If it was Lucifer and other powerful angels like Castiel fighting with their full potential, they could all destroy most if not everything in Mortal Kombat easily, with the exceptions of extremely tough and smart enemies like Shinnok, Onaga, Blaze, Shao Kahn, etcetera.
Really I thought the Elder gods in MK killed the One Reality and forced it to stay separate?
http://mortalkombat.wikia.com/wiki/Elder_gods
http://mortalkombat.wikia.com/wiki/Elder_gods?file=The_Elder_Gods.png
Notice in this picture they'd dwarf the angels in Supernatural. But it is your RP at the end of the day, so your back story.
Why not have a Call of Cthulhu-esque environment then? Particularly combining both Cthulhu Invictus and Cthulhu Dark Ages. The former has immortals that are essentially immune to normal weapons - for that you could easily read akin to Marvel Movies Asgardians, and Dark Ages which has incorporeal beings akin to angels. So it covers everything there, without the need to probe more into the brokenness that is Supernatural cosmology.
Or if you wanted a space opera with angels and demons etc then I recommend something like Alpha Omega. PM me for me details re Cthulhu or Alpha Omega.
In essence go visit Marvel or DC wikia, and a few others and copy-pasta the bits you like and world-build from there. I'm not trying to thread-crap here, just attempting to help you get a viable RP that people can understand and play.
Up to you really as you're GMing it.