The fate of Earth, Heaven, and Hell will be determined by a Heroes of Might & Magic III match.

there's no evidence in the bible about devils converting themselves into angels to serve god and help prevent humans from sinning, but it is an interesting concept that likely could exist because of the New Testament's whole moral lesson being 'Redemption'.

Plus it also seems pretty neat and fits the "What's better, to be born good, or to overcome your evil nature through great effort" thing I like.