How can I keep surprising my co-GM when he's playing in my campaign?

Question

I recently started a D&D 5e campaign with my gaming group and one of my friends has decided he wants to GM also. The setting we're playing in is a homebrew setting; I created the general outline of the map and major settlement locations and we've been filling in the details through play. He wants to use the same setting and after we talked we decided it would be really cool to run two parallel campaigns of different parties that are both impacting the world at the same time, and whose paths may cross at some point in the future. He will be playing a character in my campaign, and I will be playing a character in his. Because of the nature of our campaigns, he and I will need to keep each other aware of major plot points that could potentially impact the metaplot.

What techniques can he and I both use to keep the other guessing and engaged while still participating in the story, and without taking advantage of any metaplot details? We both have confidence that we won't use the plot knowledge advantage for any direct metagame benefits; my concern is mainly how to keep him surprised in the plot while knowing what major events might occur in the near future.

Answer 1

This is a very fun idea. Here are some of my thoughts, which you hopefully find useful. Feel free to use one or more ideas, or none if none suit your campaign.

Your Co-GM's Character Has Other Things To Do

You may both know the major things that affect the world, but your characters have much more immediate things they have to take care of; and that neither of you have to share with the other.

Without knowing details about your homebrew world, here are some examples that illustrate what I mean:

• If the next major event is an insurrection of the people against their tyrannous vampiric oppressors, one party might be a pocket resistance smuggling weapons and warfare paraphernalia; the other party might be a collection of people, meeting for the first time on the ferry away from the city, trying to escape on the eve of the rebellion.

• If the next major event is the invasion of the villain and their army, one party might be in the thick of things, present at the moment the walls were breached and witness to the fall of their kingdom; the other party might be returning to the city after the scourge has passed, coming home to ash, dust, and rubble.

• If the next major event is the return of a magical winter, one party might be busy paying absolutely no attention to it while fully knowing it's coming; the other party might be busy telling everyone they meet that it is coming.

The point is, just because you have a "shared destiny" in the world, doesn't mean you will experience it the same way, or experience the same things along the way.

Go for Simplicity

Don't decide over too many plot details with your co-GM. Go for simplicity.

Instead, set up something like "prompts" -- a small phrase that fully describes the entire core of the next "major event."

That isn't to say don't flesh out the world with him; you still do that. This doesn't mean don't agree on how the villain will ruin everything. It also doesn't mean don't spend hours designing the campaign with him.

The idea is only to set up a string of "prompts" to form the backbone of your metaplot, that roughly describe (1) what is happening, (2) where each party is, and (3) why they care about what is happening.

Design The "Major" Events Well

Imagine scenarios where, knowing what's coming ahead, when that moment arrives, each party experiences it in starkly contrasting ways. The goal is either to put in irony, serendipity, or revalation -- or something else that feels awesome.

• On the King's coronation day, one party is standing beside the King; the other is about to shoot him in the head (and get away with it)

• On the day of the villain's prison break, one party is summoned to give chase; the other, oblivious, is looking at a list of jobs at a tavern when a cloaked, hooded figure speeds past them on a horse, pursued by a party of mercenaries

• One party gets a quest from an NPC; the other party comes across the same NPC later and is revealed to be a demon

But once you've decided roughly what's going to happen next, stop there. Put an emphasis on the fact that the next "major event" affects the two parties together very tangentially, but affects the environment a lot, so both sides have a lot of room to be affected by and interpret the circumstance independently of each other.

Forget The Metaplot

Create an independent, self-sufficient story arc independently from your overarching plot. Then, at times that your private story arc interacts with the metaplot (during these "major events"), flesh out how those two lines clash and merge (but only by yourself, your co-GM doesn't need to know).

This is a good way to catch your co-GM's engagement in your story, and keep them on their toes. Because you're GMing as if there was no metaplot, they will have no way to use their knowledge to benefit themselves, even accidentally, unless they try really, really hard to break the campaign.

The Party Will Surprise You Both

It goes without saying, but you may not have to keep your co-DM on his toes yourself, because you yourself will be constantly adjusting to your players.

Answer 2

I am going to steal a military term for this: "Left and right limits" It is about knowing the 'limits' of each GM.

I have a Co-GM and player who I have been sharing the responsibilities with for years. We generally leave it up to one GM to write the "Main Story" while the other just handles "Episodes" or non-major adventures/events.

For a 'Published' world it is easier, as all of the resources are available either in book or online format. For a 'Homebrew' campaign, documentation is key to making it work. This ensures that the other GM has enough resources to stay relatively consistent within the world, but to still provide fun for the other GM.

Answer 3

I only have something small to add to the conversation, as I find markovchain's answer to be really good, but I didn't want to put the answer in a comment.

Divide the Map

I run a homebrew world where we plan on sharing DM role fairly regularly with several of the group members. One thing we have talked about doing is have a direction or map area where that DM is responsible. For example, I might have the Western part of the continent, one might have the northern, etc etc.

Shared Stories

Keep in mind that the world is a huge place (even in the same town or city) and there are likely many many plots going on at the same time, and even in the same city. You might even consider not sharing anything at all with your co-DM. This means that your BBEG can have his plot going, but when this new revelation happens, he may have to adjust his plans (just like in real life).

One side effect of running this campaign is that stories have tended to spread and so one party is spreading stories of the party fighter "Jack the Giant Slayer", and the other party hears rumors about a guy named Jack who killed a huge ogre. Feel free to use those types of things from your co-DM's campaign in your own to add flavor.

Subtle Hints

You might be planning some cataclysmic event where fire elementals raid the planet in a certain area. You may just give a subtle warning to your co-DM like 'I have something planned with the planes, so if you could avoid too much with them for a while, I would appreciate it.' This sort of thing leaves you free to work your magic, while not revealing too much information.

Answer 4

I'd do a "This is MY moment" part.

Each of you (or just you), has a 10-15 min window during the game where you and only you decide what happen in the room, or wich encounter you decide to make, or anything like that, as long as the other GM can't have any clue on what will going on.

Ask if your co-GM is okay with that, and write alone a surprise part of the story for the players, each game ;)

Answer 5

How about grabbing the metaplot and taking advantage of it? Metagaming is normally about spoiling the surprises that await your characters but it doesn't have to be. Which of these seems better?

You know vaguely what's coming up so you could try to curtail it. If you're working for the prince and you know someone is going to kill him at his upcoming coronation you could metagame your way into foiling the plot and leave your fellow party members slightly confused as to how you found out about the plot in the first place and the other GM scrabbling to find a way to keep the story going with the prince surviving to become king.

You know vaguely what's coming up so you change things slightly to set it up to be even more awesome. You know the prince is going to die at the coronation so instead of foiling it you set it up to ensure the party is there and are able to witness the event. You make sure the bard, who has been charming the prince's sister since he first met her is at her side. Will he abandon her in her time of need? What about the party rogue who has always had a troubled relationship with the prince's personal guard? When he's seen in the crowd shortly before the prince dies will he become a suspect?

Most of the time, this isn't possible because you don't know what's coming up next. Because this time you do, rather than calling it a problem and trying to stop it, treat it as an advantage and use it to make the stories you tell better because of it.