This seems like it could be OP for rushes, particularly PSN bows. I throw out my pendulums, play out my hand, then drop this. Almost all attempts to stop my rush will be worthless, and a PSN could reliably drop this turn 2 (requiring starting with 2 pends.), and by the time the spell wore off, you'd be dead.
I think keeping it at 50% even is really, really strong but 80% is just too high.