I'm drawing a blank on when exactly these kick in. I know once it becomes active you use the ability (because it doesn't say "upon activation" or "at any time"), but what about if on your next turn you want to negate a different card than the one you negated on your previous turn? Do you just simply announce that? Do you deactivate then reactivate the card? Or can you not negate a different card if the card you negated last turn is still in play? This is if GC or IotB is still active on your next turn.
