Thanks to IGN we have out first proper look at Book 2 Spirits
http://ie.ign.com/videos/2013/06/10/the-legend-of-korra-first-book-2-footage
We get to see some Nick people talk to Mike and Bryan about Book 2, they mention a few things
-Spirits can take different forms
-Creature Spirits
-Light and Dark Spirits
We see a short clip, plus some other moments all of which are very spirit focused.