Forum:Shadow Improsing Mirror

My opponent has Shadow-Imprisoning Mirror active and I have a face up infernity necromancer and a face down Infernity Barrier. Can i use infernity barrier to negate the activation of Shadow Imprisoning Mirrors effect when it activates or do i have to do it when it is first flipped face up? 173.168.59.3 (talk) 19:40, September 6, 2010 (UTC)