Combat w/ 1 player hidden from rest of group

[Tooting Dog]

Any ideas on how you would handle a combat between a Doppleganger and a player which is isolated away from the rest of the party and you do not want the combat tracker giving away what is going on and who wins? If the Doppleganger wins it takes the form of the player's character and the player would from there play a Doppleganger. The only thing I come up with is if we reach this event, I would have to kick everyone else offline in FGU and Discord and tell them to come back later. I am welcome to ideas!

[LordEntrails]

Separate session, with just you and that player. No good way to handle the mechanics you want in FG (or even in person etc), but regardless, the other players are not going to want to sit around for 45 minutes while one player fights a NPC, especially when they can not be involved in the fight and you don't even want to them to know the outcome (or probably even that it happened).

[Zacchaeus]

Make the player neutral and you can then hide hide them on the CT. Keep the doppleganger hidden. You'll need to do the targeting for the player since they won't be able to see the enemy on the CT

[damned]

Im with Lord - separate session otherwise something in chat will give it away.

[Tooting Dog]

Separate session is the only way I see this happening--booting the others so they have no clue whatsoever. Who encounters the Dopple is unknown until the party gets to this area. If I get lucky and this encounter lands at the end of our game for that day, I can later do an actual private session with the player and everything is great. Otherwise, I don't know who it will be or when it will be. But it sounds like it could be an interesting encounter and depending on which player it is and that character loses, they may actually enjoy this turn of events. Thanks, all!