Having played against this card now it feels to me that the cost to use its effect is too cheep. Simply kneeling the card to kill a character in someone elses hand can change the way you play (Confession has a better cost and is only a discard). You can't afford to keep powerful characters in your hand especially if you have duplicates in your deck as if they are killed the duplicate is then a dead draw.
This card can also create some odd situations as it is changing the rules about where you can kill a character. If I have an Aeron Damphair in play and in my hand (I will not attach the duplicate as I want him to die!) the card in my hand can be killed by Aegons Hill. Now he is both dead and alive at the same time?
I just don't know why FFG didn't make this a discard effect.