One possibility is to add a land tile that damages units. It can be on any elevation, but can't have forest or water or desert on it. This type of tiles could be as rare as mountains but could potentially give benefits to creatures from the elements deck, such as provide healing. Also DarkLegions could have a few units that can benefit from this as things from hell might like hot stuff
Well the reason why this wouldn't be unbalanced is because both the dwarves and the sylvan have a way of altering the terrain. Also maybe certain adventurous dwarves can mine flux from such tiles but take damage from it (as a form of emergency flux). Sinking Sand: hidden sand effect, if a creature ends a round on a sinking sand tile undimmed, that creature is destroyed/removed from the game. This could be built in to the game, OR it can be given to the elements deck as an enchant land... they don't seem to have things like lysis that auto destroys a creature so perhaps this helps (Then again I don't know if they do or not, I don't play elements myself)