The concept is great, but the balancing needs a little work. For point of comparison, other single turn delay cards cost no more than three unupgraded. Silence, rewind, and nightmare are all significantly cheaper. For another problem, it doesn't really do as much damage as rewind. While your opponent may not get their card back immediately, it's unlikely to be an important card because you can't target it, and it doesn't cost your opponent anything BUT that card. A card they were not yet able to play usefully anyway. Not to mention your opponent can frequently prevent the problem just by playing everything as in comes into their hand. How to balance this? We could drop the cost to 2/1 easily enough, but that's actually still weak. It could switch to hitting two cards at once, providing card advantage. This stays within the theme well, and is the solution I prefer. The last idea I have is to make it like rewind, but to let it target permanents as well. This seems a little too similar sadly, but is perhaps the most balanced method. Now, you could do something outlandish like make the diffused card shuffle back into either deck instead of just your opponent's, but I don't have any idea how to balance that properly. I think it would be the most fun way to deal with this. Entropy is well designed to use many types of quanta already anyway.
