Neutral (Not included in factions, and are fighting on their own side)
Scorpion
Skarlet (dat Shawn Kittelsen hint, hopefully she is in the game)
Kotal Kahn (LBSH)
Ermac
If Skarlet shows in the comics (hinted by Shawn Kitt) with a new design it might be a strong indicative that she is in the game too, after all, is a Story about blood magik as Shawn said it.