I really, really love this idea. One thing has me confused though. In the notes it says that it affects all immaterial creatures and the card says only enemy creatures are affected. Also, perhaps if the affected creatures were granted Divine Shield like a Seraph? Maybe call it Mass Divine Shield or something? That could also work against the player, depending on the circumstances.
Edit: read it a few more times, not confused anymore, just feel a little foolish for not reading it carefully enough the first time.