Plot The Pale Mare -- http://www.cardgamedb.com/index.php/GoTCards.html/_/beyond-the-narrow-sea/the-house-of-black-and-white/the-pale-mare-thobaw
When revealed, each player chooses 1 non-unique character he or she controls. All non-unique characters not chosen are discarded from play.
If I don't control non-unique characters(or my opponent don't control such), will plot work?
According to recent clarifications by FFG, yes.
What's the clarification, kntom? Technically the first portion can't resolve. Did they decide that when an effect affects multiple players that each player affected is a separate instance of the effect?
The clarification is that when the effect is passive (as it is here), it initiates when play restrictions say it will, whether all of the stated targets are available or not. So, whether each player has a non-unique character to choose or not, the effect initiates successfully, and all non-unique characters NOT chosen will be discarded.
(The argument was never "the first part can't resolve"; it was that the effect as a whole cannot initiate without all specified targets. FFG's clarifications were that as a passive, it does - indeed - initiate, all specified targets or not.)