One of the hardest things to do when running a game is to GM a compromised PC. (Compromised in this instance is a player character who is mind controlled, possessed, or replaced by a shapeshifter.) Taking over the character’s actions is going to result in the other PCs being suspicious so that won’t work – at least not for long. So how to do it? Here’s a few ideas I’ve used in the past.
Notes to Players
Passing notes to the PCs are a time honored tradition among gamers. In less than cooperative games the other PCs tend to attack the PC getting all the notes because they can’t be up to anything good. But notes are a good way to tell a PC they are compromised without blurting it out.
If you have good players this is the best option: just tell the PC who is compromised what’s going on and have the rest of the players react to it in game. I’ve done it this way many times and it works and lets all the players get in on it from the start. It can make some seriously memorable moments.
The best way to get a compromised player character is to give ALL the players notes with only one of them saying anything. On the compromised PC’s note you should explain they’ve been controlled, replaced, etc., why (if it’s important), what the goals of the player should be now, and any interesting information. For added fun the GM should also not know who is compromised and let it play out for all to witness. Careful, this can cause TPKs!
Sending direct messages via chat, text, etc. are the perfect ways to hand out notes and instructions for compromised PCs. VTTs make this even better as almost all of them have a whisper command and the GM can disguise what they are doing as part of the game.
Picking Over the Bones
Overall, having a compromised player character can be a lot of fun and add a lot of depth to the game. I once had a PC compromised from the first session to the end of the campaign. We were playing in Forgotten Realms and the cleric of Cyric got gecked by a doppelganger who was also a priest of Mask. Originally, the player was just going to play it out until they were found out but was so good that ten sessions later we just decided to make that their new character. It had a huge impact on my Realm’s game too because the doppelganger stole a ton of secrets from the church of Cyric by the end of the game and ran off with them leaving the rest of the PCs holding the bag. Fun was had by all, but most of the players were grumpy as hell that they didn’t figure out what was going on.