I’ve always been hesitant to use charm spells or effects against my players. First, players don’t like to lose control of their characters. And second, I don’t like players to lose control of their characters. As a referee, I have enough other entities to manage, without needing to run the PCs too.
I’ve been reading Demonspore recently though, and every shroom has charm person memorized. Shrooms are also supposed to be evil geniuses, so they should fight deviously and use all their powers to maximum advantage. If I want to run this module honestly, I need to decide how to consistently manage monsters that charm.
Here is my first idea. If a PC becomes charmed, I will give them a short brief regarding their new priorities. No more than a few sentences. Maybe I’ll write this down beforehand, or maybe I’ll just vocalize it. Then, the player will be responsible for taking actions in line with the brief. My only power as a referee will be to disallow actions that seem to contravene the brief. Attempting to twist the words of the brief, within reason, is permitted (and even encouraged) as that provides space for player skill and also models the idea that the PC’s nature is rebelling against the control. XP for particularly good adherence to the brief may be in order, but if I go that route I would like to find a way to do it that is not too subjective. Maybe something like 100 XP, with -10 XP for each time an action is disallowed by the referee? With negative XP possible?
I wonder how other people handle charm person, or other similar effects (geas, quest, etc).