8/8 FREE, PROTECTED
1. Does darken the sky (and other cards that let one unit attack twice) allow that unit to attack two different units?
2. Do hills let elevated archers shoot over your own units?
3. If you are forced to retreat, do you always have to go backwards towards your own side? What if it is blocked by enemy troops?
Yes - if retreat is blocked, regardless of what it is blocked by, each unresolved retreat space is taken as a casualty.
I'm not sure if there is a general FAQ - hopefully someone else can point you to one if there is.