New player and had a quick question that Ibtried posting in 2-player chat but could not. Earlier, I was playing someone and tried playing the Underworld card "Taken Under" with full power points but was not allowed to do so. I guessed at the time that it was because the minion I attempted to play it on was unready but now I'm thinking should that really make a difference?
Whether or not the minion was ready should not matter. If you had sufficient power to play the card, the only thing I can think of that would prevent your play (as opposed to destroying or stealing your card) would be if the target had magic immunity.