Everyone knows by now that I like to play around with the rules. This experiment was a particularly ingenious twist on the standard setup. But sadly I can’t take the credit for it.
As I recall, it was the early 80s and my friend Steve was running a game. When we all got there, Steve informed us that another friend of ours, Tim, would be helping him out. Steve would run the game as normal, but Tim would handle the DM side of all the combat. Basically, Tim was tasked with killing us. Steve would determine what we encountered. Then Tim would run the monsters as viciously as he could. And you couldn’t pick a better guy for the job. Tim reveled in his work and scared the crap out of us more than once!
It is easy to see what made the situation so much more dangerous. The DM is always the moderator; he is not the adversary. We were familiar with Steve and knew he wouldn’t actively try to TPK us. Sure he would present us with tough situations some times. But it’s the party’s job to know when they are overmatched and run away when need be. Even so, we always felt (or at least I did) that if things started going badly (through luck of the dice not by bad choices) that Steve might have the monsters make some poor tactical moves that would help us recover.
It was clear that, with Tim, there would be no reprieve. If there was an opening he would go for the throat! We all became frighteningly aware what it must be like for a tightrope walker the first time they performed without a net. It was quite exhilarating and we were all on our “A” game, making sure never to give him that opening.
I don’t think I’d recommend it on a regular basis, but I would wholeheartedly suggest giving it a try for an encounter or two.