I have only the Core Set so far and a Targaryen Plot card (Condemned by the Realm) and it's states "When revealed, choose a player. Then, that opponent must choose and kill a character he or she does not control, if able."
Person A reveals the plot. They choose Person B. Then, Person B chooses a character controlled by any player other than Person B. That character dies.
If i choose, in a two player game, my opponent, he kills one of MY characters.
More to the point, in a 2-player game, you must
choose your opponent and they must
choose one of your characters to die. So, unless you have characters that you want to be dead, it is a pretty limited plot in a 2-player game.
Then that opponent chooses ME to do the same? Resulting in one of each of our characters being killed?
Where in the world are you getting this idea? Nowhere on the card does it say the chosen player also chooses a player, nor does it say anything about more than 1 character being killed. This doesn't happen at all.
Also, in a three or four player game, how would this effect work?
In a 3- or 4-player game, you use the plot to gang up on and kill the most important character of a mutual enemy. Player A reveals the plot and chooses Player B. Player B can then choose a character controlled by Players A, C, or D to die. Assuming Player A trusts Player B not to stab him in the back, this is a good way to get rid of that power-house character controlled by Player D.
It's a plot that is designed for multi-player games that encourages players to make deals.