Quote from sleeper agent 2.0 »
We SUPER need Gix. I'd be happy with a Belbe too.
My guess for the second spoiled art was a new Latulla, Keldon Overseer (SUPER deep cut, right?!) but the video explains that it is a planeswalker. My next guess was Jeska, and after looking up the art of the pre-planeswalker version I am 100% sure it is her.
The second art is 100% Jeska. She's got both of the weapons you can see in Jeska, Warrior Adept exactly, and she has similar barbs around her face and similar clothes. Jeska was also a planeswalker between the events of Scourge (when Karona gets killed and splits back into Jeska/Akroma/Zagorka, and Jeska's spark keeps her alive and ignites her into a walker) and Future Sight (where she gives her life to seal the final major rift caused by Karona and start the great mending).