Here's the background - one of the players have to leave town for an exchange programmee lasting 6 months, but I have already filled his slot with another player. We are thinking of ways to include him as a co-GM in my game.

Searching the Internet doesn't yield any advice on how to have a co-GM in the game. I am hoping to incorporate the co-GM as more than just a helper during combat, but I am falling short of how a co-GM can contribute in a game (besides splitting up the party).

Is it feasible to have a co-GM in any meaningful sense, and if so, how?

On reviewing the comments:

  • By co-GM, I don't mean "multiple GM". I still think of myself as the "lead GM", setting the direction of the campaign, determining who are the major enemies, allies and events of one session.

  • There are various duties a GM can have, including

    • Role-playing NPCs in out of combat scenes
    • Playing NPCs in combat scenes
    • Adjudicating dice rolls and rules
    • Deciding the direction of the game and plot
    • Reacting to players' intent and spontaneous actions

So I guess the question is, how I can share those roles with another GM, while maintaining consensus when players try something new which we haven't planned for? We could decide on the NPCs' motivations, the scenes, the outline of the session and so on, but how do we improvise on the fly together without breaking the flow of the game, like taking a ten minutes break to confer with each other?

For further context, the system I am using is 13th Age.


4 Answers 4


To begin with, you should see what are the strong sides of yours and your co-GM candidate and try to make use of those aspects of your GMing in order to compensate the weaker sides of each other.

Let me provide some orthogonal aspects of a good GM I see over years of playing games. You can even stylize those as a list of abilities and make GM-sheets, rating each others' abilities in the areas of interest.

  • STR: Storytelling. Shows how well can you use the language to speak about events, how detailed and colourful picture of the surrounding world you can inject into players' heads. Also, describes the overall interestingness of your modules and campaigns.
  • PRP: Session and module preparation. Shows how well you are able to prepare to a session, how detailed your module is, etc. Can be thought as "playing against players". You need to make challenges, puzzles and the storyline in such fashion that it's not a cakewalk for the party.
  • IMP: Improvization and adjusting the plan to the events that ocurred. One can think about this one as "playing with players". Shows the degree of interactiveness of your world.
  • RAW: Rules-as-written. How well do you know the rules as written and erratas from the main books, complementary books, et al.
  • GLD: The Golden Rule™ usage. Are you good at making decision of throwing in the Golden Rule™? Can you handle munchkins? Those are things that this ability shows.
  • PXP: Playing experience. How many campaigns of the given system have you played? How well can you understand your players? This is yet another "coodrinate" in our system.

As a rule of thumb unless you have a large experience of GMing together you want to divide the roles and as the main GM, you want to have STR and PRP on you.

Here is a suggestion that's supported by my own experience: If you want to run a session or two with co-GM with little to none preparations, just let your co-GM run some key NPCs (making use of GM's high IMP ability); let your co-GM to calculate the combat (making use of his high RAW ability) and finally let your co-GM to decide for NPCs in combat (if he has a high PXP score in addition to a high RAW score).

As for the question about collaborative improvisation I would strongly suggest against it. You shouldn't do that until you are sure that you understand each other perfectly and will not mess up with each other's plans, bringing discord in your game. However, over time, as you talk more about the campaign and get better synergy, you'll be able to offload more creative tasks to your co-GM if you two will wish so, including improvising together.

An example of collaborative improvisation would be a case when you — as a GM — need time to think a little bit about some tweaks to the storyline on the fly. In order to do that, just signal co-GM to take over and (given that you understand each other well enough) you'll be able to retake mastering of the game after you have made all the tweaks you needed.

Hope that helps.

  • \$\begingroup\$ Which golden rule? The GM is always right? Do unto others as you want to have done unto you? The game should be fun? \$\endgroup\$ Jun 19, 2014 at 11:06

Yes ... well maybe ... wait No... How about all three?

It all depends on what you mean by "meaningful sense". But whatever that is, the key is communication between the two GMs. Everything else is fluff. With good communication, you get better consistency, better cohesion of the world, and better world reactivity. With bad communication, you get no where.

Most of the time when I successfully co-GMed a game, we had a lot of pre and post game discussions to make sure we were always on the same page. We both had a very good understanding of the meta world. While co-GM helps during a session, you have to do a lot of extra work outside of it.


In my experience co-GMing can work really well so long as you agree jurisdictions before play. For collaborative improvisation this comes down to agreeing what the subordinate GM has authority to do in the game world.

I have found that it's easiest to delegate a subset of the world to another GM while keeping important plot parts of the fiction with the main GM.

This can be giving the co-GM control of a third party faction (e.g. controlling the goblins in the camp) or giving them responsibility for the general population of 'normal folks' or 'independent monsters'.

In effect the co-GM can play a role much like that of an elevated player in that they have their NPCs react to the unfolding narrative much like the players must - not knowing what's going to happen next.

This way the co-GM if free to improvise within boundaries which the lead GM sets. As you get more comfortable running together you may decide delegate more responsibilities, which can work very well in a 'play to find out what happens' style of game, but I'd be cautious of handing out too much control to someone else if you have a plot in mind because it's very easy for the co-GM to break parts of the plot unintentionally (unless you pre-plot the whole thing together first).

In most games, one of the key responsibilities of the GM is that of scene framing, much like the director in a movie cuts a scene and sets a new one - for example the GM can decide to skip ahead over a long journey to a point where things get interesting again, - this gives a lot of control over the pace and direction of the game. In my experience, this power should always remain with the lead GM. Sharing scene framing responsibilities with another GM can easily lead to a loss of cohesion in the narrative thrust of the game and makes the GMs job significantly harder.

  • \$\begingroup\$ Welcome to rpg.se! This is a great first answer. \$\endgroup\$
    – okeefe
    Jun 19, 2014 at 13:34

I'll give a bit of experience here. I was PC in a 2years campaign in Anima : Beyond Fantasy, where we had 2 GMs. The concept of their strategy was that they would switch the main GM role and the other one would play a PC of the group. The interesting thing, is that they use this PC (called Macara) very differently, only for us to discover that it was planned as Macara was in fact Schizophrenic.

Moreover, when preparing a session, they would NOT tell the other GM what was going to happen in details (even if they both had main plot knowledge) so that the PC Macara could react very naturaly.

When they needed both GMs to to the GM job (RP heavy scenes), they would trust each other to play a NPC, and if they needed confirmation would simply ask the other GM.

It was extremelly pleasant as a PC, so I hope you can salvage some of these ideas for your campaign.


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