I've always thought of Omega as looking something like a hydralisk--biological and alien, almost a scaled-down Lovecraftian horror.
(Necro-thread)
I can't explain why, but I've always imagined Omega to be a big hovering red sphere with a cartoonish face, and black beholder-like eyestalks coming off him from all sides.
He may have been influenced by the Flying Spaghetti Monster.
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