Be aware of SPOILERS from all kinds of movies. All and any players may post their theories.
X-Men Theory:
This is what Raven (Mystique) saw that made her cry in Days of future Past. http://vvcap.com/6IidPjB5TmN if you've seen first class, you'll know who it is. A.zazel. He was one of Trask Industries mutant subjects. It probably killed him or something. How did i find out? I looked up Night Crawler A.zazel images. This is as close as i could get for Nightcrawler: http://vvcap.com/Dbj6NF5dKOa
Star Wars Theory:
Mace Windu is still alive. It never showed him die. It showed him fly out the window, yes, but we never saw his body. https://www.youtube.com/watch?v=e-0UXhBN26E
Look at the scene it shows Snoke. About at 1 minute 55 seconds. See the purple around him? He uses the light and dark sides like Mace Windu did. More proof here: https://www.youtube.com/watch?v=mAIdbuqLCto Kylo Ren knows his signature move. Mace was the only other Jedi or Sith that used it. So no doubt in my mind it's Windu.