To recall, the first two abilities of Nicol Bolas were already revealed but not yet his ultimate ability. Here he is with the complete abilities. Behold!
Nicol Bolas, Planeswalker - 4UBBR
Planeswalker - Bolas
+3: Destroy target noncreature permanent.
-2: Gain control of target creature.
-9: Nicol Bolas, Planeswalker deals 7 damage to target player. That player discards seven cards, then sacrifices seven permanents.
5 Starting Loyalty
I don't know of his rarity but I'm pretty sure he is a Mythic Rare.
Edit: They've posted a video of the actual tip card, which confirms he is a reliable source. Check it out below.