There are several situations that prevent you from targeting a character with Yoren. RRG page 22 and FAQ 1. 3
- If you OWN a unique card in play, regardless of who controls it, you cannot marshal/play/put into play/take control of another copy of that card - except as a duplicate (if you own & control all instances).
- If a copy of a unique character is in your dead pile, or the deal pile of the owner of target character, you cannot attempt to bring into play a copy of that character.
- If a character changes control and subsequently leaves play, it goes to it's owner's out of play area. So for example, if you borrow The Hound, and his Forced reaction kicks in, The Hound will go to his owner's hand.