Shadow Jago has been in Killer Instinct since the game launched, but up till now he was pretty much just an alternate skin for Jago since they both have the exact same move set. Things change a bit when they made Shadow Jago a secret boss at the end of the Season One story mode. He still had normal Jago's moveset but he also had a special ultimate combo that no one else has. Starting later this week however Shadow Jago is getting a huge makeover and will be getting his own original moveset.
It seems that Shadow Jago has been given a low slide, air fireballs, a teleport and a diving high kick. What I find interesting is the end of the trailer where it's unclear what combo Shadow Jago is performing. I would think it's ultimate combo since they usually end these trailers with an ultimate. In this combo the screen is completely black and plays out more like an ultimate combo, so i'm wondering if that is some kind of tease that the season 3 cast will have ultimates. Again, that is just pure speculation from me. Hopefully we will get some more news about season 3 soon as it's set to launch in the spring.
For anyone who already owns Shadow Jago, he will be available to play on December 4th. For anyone else, he will be available to purchase from December 18th - January 15th. After that however, Iron Galaxy says that it's unknown if he will ever be available again.