In the preview, a voice-over is heard with the oath of the God of Thunder as the new supreme ruler. We see a clash between Thor and the enemy army, in a world that is neither Asgard let alone the Earth. We see Chris Hemsworth wielding his hammer and Tom Hiddleston as Loki first wounded without a helmet, with long, loose hair and then imprisoned; his anger increasingly desperate and irrational. Then there’s a scene later in which he is free again, but still furious.
The hair got longer…Awwww Yisssss!
Of course you have to take these reports with a grain of salt, the info could be wrong, or scenes could get cut/edited out, etc. However I do hope this is 100% true!
(source: Read more at http://www.comicbookmovie.com/fansites/MarvelFreshman/news/?a=70953#AoQCuhOmAV51bApO.99 )