The Two Watchers
The Mountain of Fire#70 (x1)
Location
X (-)
Mordor.  
Immune to player card effects.

X is twice the stage number of the main quest.

Forced: After the players travel here, flip The Two Watchers to its enemy side and move it to the staging area.

They were like great figures seated upon thrones. Each had three joined bodies, and three heads facing outward, and inward, and across the gateway.
-The Return of the King