Mistfall was a successful Kickstarter last year which aimed to bring an RPG adventure into a card game, much how Paizo brought the Pathfinder RPG into a card game. In Mistfall you pick a hero, who comes with starting equipment and skills, and then take him on a quest of your choosing, battling monsters, upgrading your gear, and leveling up as you go along.
Mistfall: Heart of the Mists aims to essentially give you a base set again, but with all completely new heroes, monsters, quests, and gear, allowing you to either start with this set or mix it with your base set for nearly double the amount of variety. The expansion will be Kickstarted like the base but no solid date has been given, however, they say soon so keep an eye out for the announcement. You can read about the expansion and look at some of the new art and components on the NSKN site.