Fell Beast
The Flame of the West#57 (x2/x1)

When Revealed: Attach to a Nazgûl enemy. Limit 1 per enemy. (Counts as a Mount attachment with the text: "Attached enemy gets +1 , +1 , +1 and -10 engagement cost. Forced: At the end of the round, return attached enemy to the staging area.

...horrible as carrion-fowl yet greater than eagles, cruel as death. -The Return of the King