[RPG] How to fairly knock a player unconscious for a doppelganger swap?


I am DM'ing a D&D 5e campaign online using Roll20, and I want to introduce a section where a PC is swapped out for a doppelganger.

I have come up with a plan/scenario where a character can be separated from the group for the swap-over to happen, but I need a way to knock the PC unconscious for a few rounds — in a way that seems fair, quick and with the minimum of fuss. As the game is online, I can do the swap without the other players being aware of what is happening, so the doppelganger plays the part of the PC, and then in the first battle, starts attacking the other PCs.

(Meanwhile, the player will be in on it, and play the part of the doppelganger 'til I give him the wink to start attacking the other players.)

I was thinking some form of gas, sleeping darts or similar – but then we get into saving throws which the other players with see – so that wont work.

How can I fairly knock the PC unconscious? Would it be fair to have an automatic knock out without any saving throws? Would it be fair to fire 20 darts at them, each making the player sleep for 1d6 rounds if they hit?

Best Answer

If the outcome is already determined and the player of that character knows about it, you don't actually have to cover it with any specific rules. Simply tell the other playes they got separated from that one character and later he rejoins them without anyone knowing what happened inbetween. When they later get the actual character back, he can simply tell them that he only remembers going down a hallway and next thing he knows he was in some kind of cell or something like that.