How can I run a session where two opposing parties play at the same time?

Question

A player of mine had an interesting concept where two parties who are opposed to each other would play at the same time in the same session. In essence the plot would be a group of thieves have been hired to steal some kind of magical artefact from a castle, and the first part of the session would be this group infiltrating the castle and getting to the artefact.

Once they remove it however, of course alarms will go off, or a pair of patrolling guards will see it's missing on their next rotation. This would then introduce the second party who are a group of elite guards.

I was thinking the easiest way to run it would be to give each group 30 seconds to decide their course of action, and then act upon it. The guards will have a map so they can point out to the DM where they want to move next, and the thieves will have a map revealed to them as they travel along that they can point at to try and avoid metagaming as well as other punishments for metagaming. Naturally the two parties will be at opposite ends of the room.

How can I run a session like this where there are two opposing parties in the same session?

All the players have shown a lot of interest in trying this idea out for a one-shot. I am hoping to use some online resources to help run it; any specific ideas are welcome, but should be supported by experience (per Good Subjective, Bad Subjective).

Answer 1

Sounds like Epic Adventures from Adventurers League.

D&D Epics are exciting multi-table events where participants cooperate in a “mass raid” of truly EPIC proportions; as every table works toward the same goal, individual tables act as squads that might take on different tasks, possibly affecting other tables or unlocking side quests needed to progress the event.

An Epic Adventure has a structure consisting of 1-hour missions, each played by a different table. Every mission has a different objective and grants different bonuses when completed. There are also events that, when triggered, grant immediate bonuses or penalties to all tables.

You need another DM

Each table has their DM, so they can play simultaneously. You need to have another DM to take care the other party and communicate if the other party affect your party ("The guards successfully turned on the emergency light, your stealth rolls now has -2 penalty").

However, if you are planning to solo DM, I suggest to convert the "hide-and-seek" showdown to a combat showdown, ended with either the capture of the thieves or their escape. It is more manageable, without losing the narrative conclusion.

If your group is not into combat, you can change it to a skill showdown.

1. Gives each party 3 objectives that are solved by skill checks against DC or other party's opposing check.
2. Each party takes turn to complete objectives.
3. Each successful objective grant bonus or penalty to subsequent checks, to you and your opponent, respectively. This mimics "events" in the Epic Adventure.
4. Each successful objective also grant bonus or penalty to the final skill contest.
5. Final skill contest is whoever wins three times first, win the game.

Using this method, you as the DM have to adequately interpret and narrate the result of their checks to build the tension toward the final skill contest.

Last note, "hide-and-seek" with traversing the map round by round will be tedious and takes a lot of time, even with two DMs. That's why I suggest you to ditch the hide and seek and use alternative.

Answer 2

While I think the answer detailing the Epic Adventure mechanics above is great, I also think that coming up with a second DM can be a little difficult for us home players. Considering this is going to be thieves versus guards, with some non-combat obstacles [i.e. skill tests], some random encounters, and some fun complications, my first thought was to suggest using the Chase Mechanics found in the 5e DMG on page 252. These leave a little bit to be desired, but are certainly the bare bones for what a DM can use to customize into their own adventures. Here's what I suggest:

Building the scenario as a Chase (keep it simple!)

First you'll have to decide if each player at the table gets to run their own character on the chase map or if you will have them, generally, work as two teams. So, will each player have an initiative or will it be one initiative per team? Will a skill check be made by a single character or by the team? Does the team or individual characters take the levels of exhaustion for failures? etc.

1. Map it out: Where, What, How, When

   • Where will each team start? In your scenario, you can know where the guards will start and where the quarry of the thieves is--but the thieves might have a choice of entry point (adding a little bit of flavor!).

   • What obstacles are you going to have throughout, in otherwords build your map and also your own Chase Events--i.e. where are the skill checks & what are they, where are the random encounters/built-in encounters & what are the.

   • How will both teams interact with these obstacles the same way? The elite guards might have keys to doors but the thieves can crow-bar or pick the locks quickly. An encounter met by the guards first might mean more guards on the way for the thieves; conversely, if met by the thieves first...they may already be dealt with (or circumvented!).

   • When will things extraneous to the chase happen--for instance, when will the general alarm be sounded once the theft has been discovered (2 rounds? 5?).

2. Initiative - Determine it. Most likely, the thieves will go first because they'll already be on the move--but this could depend on earlier choices and, of course, dice rolls.

3. Track Movement - The rules, for me at least, are a little bit clunky here and take some working out. This is an interesting suggestion for a Chase Track, also see this discussion on the Chase here on StackExchange. I suggest:

   1. At the start of each leg, both sides choose one character to represent them. The two characters make an opposed Strength checks (adding Athletics). No character can make a second check until all allies have made a first check, and so on.

   2. The winning side widens or closes the gap by d10 feet per 10 feet normal movement rate of their representative (rounding up). Eg: a 25 feet movement rate = 3d10 feet.

   3. If the PC scored an odd result on the Strength (Athletics) check, then the PC encounter a Chase Event! If the PC scored an even result, the other side encounters a Chase Event! Don't be shy about building sure-thing event (i.e. this encounter with a difficult lock will happen here, no matter what).

   4. Repeat until the chase ends.

4. Track Exhaustion - The Dash action can be used a number of times equal to 3+ your Constitution modifier (for a team, I'd take 3+ lowest Con because you can only move as fast as the slowest party member). For each Dash action after that you must succeed on a DC 10 Constitution check or take one level of exhaustion. Your team/PC cannot move once you've hit exhaustion level 5.

5. Pursuer Overtakes Quarry (Guards catch thieves) - This isn't in RAW, but since you have actual players playing both sides I'd offer the guard group catches up to the thieves give them an option to attack, perhaps at a disadvantage, or overtake (grapple) which would stop the movement of at least two PCs if not both teams, until grapple is escaped (if it's escaped!).

6. Quarry Eludes Pursuer - The quarry can attempt to escape if it is out of sight for all of the pursuers. He makes a Dexterity (Stealth) check and must beat the passive Wisdom (Perception) scores of the pursuers.

7. Complications - Roll 1d20 at the end of your turn and compare that roll to the appropriate Chase Complications table (preferably one that you've come up with). Now, if you have two teams, then the complication would, logically, be applied to the rolling team. If individual PCs are rolling then, as per the rules, the complication is not applied to your character, but rather to the next character in initiative order. Either way, an inspiration point to negate the complication you rolled or one that effects you.

   This guy has created some custom Chase Complication tables that you could easily adapt for yourself.

This is a smattering of RAW and home-brew because it is altering the chase to incorporate two teams of PCs. Suggestions and edits are welcome!

Answer 3

Back in the day, my friends and I had a game where one of the PCs decided to contest the party's leadership. This quickly led to the other PCs taking sides and entering into semi-open warfare between the two factions.

The DM didn't really use any special techniques to handle this, aside from going into another room with any individuals or groups who were doing things which they didn't want to be common knowledge, such as setting traps or wards to inhibit the other faction.

Also noteworthy here is the technique of note-passing, for smaller private communications which don't warrant going to the trouble of moving into another room. We didn't use notes in the specific case I described above, but I have used them on many occasions in many games, sometimes in conjunction with "fake" notes that have innocent or meaningless content so that other players can't conclude anything purely by knowing that a note was passed.

In your particular situation, as the GM, I would start out with the two groups of players in separate rooms and move back and forth to handle each group in turn as they moved about, trying to find each other, then bring everyone into the same room once they made contact and the characters in each group became aware of what the other group is doing. Once everyone is together, you can continue to make short trips to the other room with groups of players or pass notes to still allow hidden movement/actions or secret planning.

This approach is also somewhat similar to the technique used in the Braunstein games which led up to the invention of D&D, although Braunsteins did it the other way around, with the referee staying in one room with the map table and the players coming in and out for each turn.

Answer 4

With two opposing parties the game will go painfully slowly for both.

The Basic loop of D&D is:

1. The DM describes the environment.

2. The players describe what they want to do.

3. The DM narrates the results of the adventurers’ actions.

One party is going to be on hold while you're narrating for the other as the game can't proceed without a DM. This means both sessions will proceed haltingly.

The style of play you've described does not seem well suited for D&D. This style may be easier to execute under a different gaming system.