I nice expansion for 5 Leagues, and I find it quite compatible with the 2nd edition, with really nothing to change.
Basically what is different is the encounters tables, and the after battle loot and such.
You have "Fey" creatures, which some items affect more, and others don't affect at all. Hope you have the right things!!
Areas tend to be more dense, so there will be less ranged combat, more up close and personal stuff. There is only one village, that helps.
There are new (and strange) type of enemies, many not quite human or plain not at all human.
If you want a more "spooky" adventure, this is for you.