“Heroes of Might and Magic V: Tribes of the East”

Judging by the plot, the Elves will be Elves - Elementalist, and the Dark Elves will worship demons, so the alternative upgrade will be related to them (but these are just my guesses).

I agree with you about the Dark Elves (I'm simply not interested in the Forest Elves); personally, I imagine the alternative upgrade for the Twilight Dragon as looking black, but with red-orange hues and glowing.