Reeking Moat
The Mountain of Fire#29 (x3)
Location
2 (4)
Plains.  
Forced: After Reeking Moat becomes the active location, choose a non-unique, non-Nazgûl enemy in the staging area and place it facedown under Reeking Moat.

Forced: When Reeking Moat leaves play, put each enemy under it into play engaged with the first player.

...towards Mordor lay like a moat a great mire of reeking mud and foul-smelling pools.
-The Return of the King