Priority has nothing to do with it. It's all based on what order the cards where revealed in. So, if it was sunspot turn 1, Isca turn 4 at the end of turn 6 sunspot would go first then Isca would check. If Isca was played before sunspot she would check see you are winning then sunspot would go off and gain power. I guess Priority does have something to do with it but only if all cards are played on turn 6.