L3333- Yeah, I am not particularly familiar with the cards in Standard (besides sets 7-10). So thanks for pointing out that card. It seems like that could be devastating.
What if it was "becomes exhausted" rather than exerts? Then there is the little bit of a let down in that they cannot be assigned to a skirmish so the Shadow player can't kill them (via a skirmish, at least).
Exhaustion seems flavorful enough. I'm sure Boromir was tired as #$&*@! of all of Frodo and Gorn-bot's #$&*@!.
-wtk
Edit: I think it would have to be "unbound companions," by the way. Probably not good to prevent Frodo's skirmish...