Dark Ascension is a new talent we're trying for Shadow. The version currently on beta is an unfinished, in-progress version. The implemented version we have internally is currently:
Dark Ascension - 1 min cooldown, Generates 50 Insanity, 40 yd range
Immediately activates Voidform, then releases an explosive blast of pure void energy, causing Void Eruption damage to all enemies within 10 yds of your target. Cannot be used while in Voidform.
Tuning is pending playtesting/feedback, but the goal is to give Shadow a more controlled way of entering Voidform.