Everything that is playable with nightmare atm is exiting my interest. So is this. I'm just not sure with the mechanics. I f you play prion a brain rot is generated in your opponents hand and the only way to get rid of it is to destroy the permanent, right? If it's the case I don't think that the limit of 3 is necessary. You can still play with 6 slots taken and you can destroy the permanent to get you slot back. Moreover, it becomes interesting to play IMO if you pass the 3 slots occupation. So the cost is very hight if you can not even have a real effect out of it.