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I think you are all a little too slaved to the game mechanics... When I hear something that starts by: "if it is not in the rules..." my ears start to bleed. The rules are all guidelines and the DM can change them as he sees fit. If you aint happy with that possibility, then move on. However, I *hate* DM who are actively against the players to the point of being unreasonable but a sore is at most a funny plot twist.
Furthermore, I guess you must have a lot of friends to play with, because I couldn't just go off on one of my best friend who also happens to be my DM. We usually discuss it and come to an agreement and its the end of it.
Finally, I could share some of my past experiences where I really made a PC flip out of his mind with mind tricks. As I mentionned, not everything is in the rules and this is a perfect example:
One of my player had been possessed by a devil during a previous encounter. It was a very cunning and subtle devil and I decided to play it out to the extreme. While the possessed went to get a drink refresh, I told the rest of the party: "whenever I do not have my glasses on (I wear glasses obviously), you do not hear or see whatever I tell player X (the possessed player)". The group did not know why I was doing this, but they had some sense that something was off (which was perfect by my book) and they played it out like champions.
We did a few games like this until they could confront the evil, but it was a very refreshing experience for all of them especially the possessed player who definitely thought he was going insane at some point. Everyone had fun and that is what matters.