Pulled this from Reddit, so grain of salt and all (concerning Vader):
He is in the film briefly throughout but he becomes more prominent at the end. The team are running through the ship and there are no lights (very atmospheric, the cinematorgraphy and lighting is fantastic). Chirrut suddenly stops and is in pain, then says "he's here." Then we hear the breathing, none of the team know where it's coming from (it's very dark). It's like a horror scene, like nothing we've seen in a Star Wars film. The breathing gets louder and louder as Vader gets closer, this literally goes on for minutes, the tension was unbelievable. Eventually the space is illuminated by Vader igniting his lightsaber and the slaughter begins.
If this is true I'm gonna lose my shit when I watch this scene!!!
So much like Jason Vorhees or some other Horror Charachter that stalks it's prey,which i want soo badly, but judging by Pablos twitter it looks like some of the reddit spoilers are false also, either people misremembering or they never saw it to begin with, also still hearing no lightsabers which leads me to think this ones false
But i hope hope hope it's not false, i wanna see Vader Wreck fools.