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?

  • \$\begingroup\$ Are you asking for a method of knocking a PC unconscious without them getting a saving throw, or are you asking if an automatic knock-out without a saving throw is fair? \$\endgroup\$
    – Miniman
    Mar 15 '15 at 12:15
  • \$\begingroup\$ What will the replaced player do in the meantime? \$\endgroup\$
    – nvoigt
    Mar 15 '15 at 12:46
  • \$\begingroup\$ The player will play the part of the Doppleganger till I give him the wink to start attacking the other players. I am asking if making a PC unconscious without a throw is fair, or if there is a method that will work which makes it fair, which does not involve a saving throw. For instance, if I have 20 darts fire at the PC which rolls for attack, and if they beat the AC they strike, which means 1hp of damage but the character falls asleep for 1d6 rounds of time - does this work, and is it fair? \$\endgroup\$
    – Jaffa
    Mar 15 '15 at 13:12
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    \$\begingroup\$ Please indicate what equity framework you wish us to use (Randian, Rawlsian, Kantian, Marxist-Leninist, Classical Liberal, Augustinian, Confucian, etc) or indicate you want an overview of the topic or a reading list or something like that. You may find this question better answered at Philosophy \$\endgroup\$ Mar 15 '15 at 17:10
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    \$\begingroup\$ @thedarkwanderer Seconded. Fair is a difficult, fragile, pregnant term. I urge the querent to scrub fair and replace it with mechanically or even legally (as in rules legal). \$\endgroup\$ Mar 15 '15 at 17:26

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.

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    \$\begingroup\$ While this advances the story, unless players can narrate the same sort of event happening to their foes I don't think this meets the standard of fair. \$\endgroup\$ Mar 15 '15 at 14:39
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    \$\begingroup\$ Who would be treated unfairly? If the outcome is predetermined, then it does not become any less or more unfair if the GM introduces some kind of super poison gas that allows no save and of which the PCs will never find another dose anywhere. \$\endgroup\$
    – Yora
    Mar 15 '15 at 14:46
  • \$\begingroup\$ @HeyICanChan Looks like a frame challenge. \$\endgroup\$ Mar 15 '15 at 17:47
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    \$\begingroup\$ @HeyICanChan I think the challenge is "since you're predetermining this, skip attempting to fake fairness". The question asker wants to be able to do this 100%, but wants "fair" so they don't feel guilty. Skip the dog-and-pony show and get right to the collusion with the player avoids it better. \$\endgroup\$ Mar 15 '15 at 18:08
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    \$\begingroup\$ @SevenSidedDie Okay. I think I understand. The unfairness I see is in the initial removal of player agency ("During the cut scene, your character is replaced by a duplicate"), but, if allowed by the social contract, that's neither fair nor unfair but just the way the campaign's managed. So while I would leave such a campaign, others don't find that removal of agency the violation that I do. Fair enough (literally). \$\endgroup\$ Mar 15 '15 at 19:50

For spells, Power Word Stun does not allow the player to make a save. This should be a long enough stun to allow the NPC to tie up the PC or knock them unconscious.

If the player does not have trap sense, you can always use a trap to apply some sort of sleep affect. Fuss is usually created when the player feels his characters life is at risk, so if you do not have an enemy present, and instead it is just a form of sleeping gas, the player is more likely to be okay with it.

For these sort of scenarios, I would keep it strictly role playing. "You feel a blunt object smack against the back of your head for a split second, before the lights go out...". Out of game: "Okay, your character has just been knocked un-concious, don't worry, no harm has come to your character, this is an event that triggers in the story line when the party gets split up. For the next couple of scenarios you will assume the role of a doppleganger with this goal in mind..."

From there you can add in your own twist depending on how the player reacts. Say for example, the player does not like the idea of back stabbing their own teammates. Tell them that off on the side they will have the ability to attempt to escape, and potentially make it back to the party to warn them just in time. The ways in which you can avoid conflict between 'fair' and 'unfair' scenarios is endless based on how you word things!

Also, saying they got shot by 20 darts, and have to make 20 fortitude saves to avoid being put to sleep is a bad idea. Why? Because you are trying to justify an inevitable situation with an in-game rule. You give the player a glimmer of hope and waste their time in saves just to take it away from them anyway.

I had a scenario similar to this where our group ran into a Naga caster. It had already felt like the DM was out to kill a specific party member, and sure enough when the Naga used mass charm the only person to save was that targeted party member. The DM then continued to spam sleep spells until that solo character eventually failed. He then had the charmed PC's go to the Naga's house while the Naga said "I'll be right back, please wait here" and then performed a coup-de-grace on our party member. As players we were not allowed to attend to our sleeping friend because "that was meta gaming" and "you see the naga as friendly, you have no reason not to listen to her request" thus we could not leave her house or avoid going to it in the first place. In the end that solo player succeeded on a total of 6 DC 17 saves, and died because of it and was in fact punished for succeeding the very first one. Moral of the story: Don't give the players saves if something is going to happen to them inevitably, that is a dick move (Also don't make killing them inevitable).


In 5E, the "KO" is declared the moment you run them out of HP in melee; there's no need for anything else. So, depending upon level, it could be the doppleganger, or a rogue hired by one to kidnap them.

The prerequisite for the swap isn't the KO, but the others not seeing the swap. Which basically means needing to snatch-and-remove...

As to the fair part - if it's done as part of an encounter not more than the deadly amount, it's pretty much a "fair" encounter, in the sense that the party has a chance to triumph.


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