Once part of Santa Ana's Mexican Legions, the Lost Army was dispatched northward to investigate a mythical 'black rock' with magical porperties found up in the hills. Presumed dead for over 50 years, they have now returned with a burning hatred for the living and their full complement of siege weapons, now twisted into thunderous and deadly Hell Cannons!

Each of the Mission Packs offered in the Add-Ons menu is a themed adventure set including a new Enemy type, new cards themed for those Enemies, a set of new Missions involving them, and a new Objective Room Map Tile that, like the other map tiles in the game, is double-sided. It has an Old West Mine side and an OtherWorld side, both for use with the themed Missions of the set.