Slopes of Cirith Gorgor
The Mountain of Fire#28 (x2/x1)
Location
4 (1)
Hills.  
Forced: When Slopes of Cirith Gorgor leaves play. the first player shuffles the encounter discard pile into the encounter deck and discards cards from the top until an enemy is discarded. Then, he puts that enemy into play engaged with him.

...they knew that all the hills and rocks about the Morannon were filled with hidden foes...
-The Return of the King