I don't know if it was a good idea or not, but it's too late now.... I'm having two campaigns clash and I know that a fight will occur.....

Is there a way for me to track that fight in the encounter tracker from beyond? Or do I have to go back and forth on different tabs or go with pen and paper? I'm a bit at a loss as to how to manage it. Especially if I have players missing that night.

I think you're asking whether the encounter builder and combat tracker support player vs player combat.  I believe the answer is no, unless you want to homebrew monster stat blocks for one of the parties, but there may be tab juggling work around for that.

Yes, that was pretty much the question. That's what I was afraid. I guess that game will be management heavy then. Thanks for confirming the info.

I've done very little PvP in 5e myself, some folks are really against it and have all sorts of math about how 5e's mechanics make PvP "broken".  Since I don't see it much in my games I've never really paid that much attention.

If I were you, I'd lean into the players doing the bulk of the management.  I mean it's their sheets and all.  In this sort of event, I think the DM is best as initiative tracker and settler of rules disputes and otherwise let them fight it out.  Despite the mechanical concerns I mentioned that I don't really follow, I think PvP only works if the players really know their sheets.

Coincidentally last nights Critical Role was a guest battle royale, where another cast member (Sam Riggle ... I don't really watch it, it sorta came on my feed last night) ran five players through a everyone vs. everyone and the environment scenario.  When it's posted for view on demand you might want to skim through some of it to see how it sorta plays (with the caveat that the DM admittedly wasn't much of a rules guy, like seriously did not seem to understand how attacks of opportunity worked).

Seconding MidnightPlat on letting the players do the bulk of the management. Just as a friendly warning, the absolute worst session I've ever played in, by a country mile, occurred when the DM had us fight his other campaign and didn't give the players enough agency. It was a disaster. (It was also ridiculously one-sided which made it so much worse, so hopefully that's not the case with your group.) I think setting up expectations ahead of time will also be a huge help. Best of luck!

Without going down the "what if" rabbit-hole, this sounds like a lot of opportunity all balled up into a teeny-little-space. 

• Sitting the two campaigns down at the same table or same session might go poorly, as the point of this fight is to kill off a PC or several. People will more than likely be passionate about this.
• If you have the time, I might suggest to create NPC statblocks from the PC sheets and run the "bad guys" yourself so as to keep the campaigns seperate, and to allow two separate outcomes versus just one. Two separate outcomes could match up to be the same one, but there are more possibilites if you are running the "bad guys".
• Other side of this might be that you didn't portray the "bad guys" characters exactly as the players would have and potentially have them fighting a party that they may not fight at all. Diplomacy is a form of conflict resolution.

If the parties are equal level, expect that one party will be completely wiped out dead by turn 2 or 3 of the combat. The smaller the party, the more likely this is.

Let's say that each party has 4 members. If one party wins initiative for the first 3 turns, they'll likely drop at least one of the opposing party before that character gets a turn, which will cause a snowball effect. As soon as one character is down, you have only 3 turns compared to the other party's 4, and are less likely to drop one of them, or they'll have to try to spend a turn casting Healing Word or similar (wasting a turn of damage) to get them back up. This then continues to snowball. If the first 2 players to take turns are on Team A, and they have access to big AoE spells like Fireball, then this is an even bigger problem.

Rather than coming down to last man standing, it's likely that the party that loses initiative dies in 3 turns without inflicting much damage back.

At higher levels, this may sound less likely, but Hold Person cast at high level on the first turn of the combat could mean things are over on turn 1.

Wow! Thanks for all the answers. It's really eye opening. I like Kaavel's point about creating friction between players. Knowing my players, some might find it hard if they end up losing their character. Even if they stated that they wanted a PVP to raise the stakes.

I think that playing the other campaigns characters for the fight myself would be better. Because nobody loses actual character and they can always blame me for not playing it well. (DMs responsibilities, I guess).

But that puts me back to having to manage multiple characters with much more things they can do than monsters.

I guess I'll end up having a lot of coffee and muscle through it. 

I don’t get what you as DM would need to manage. Beyond tracking initiative and making rules rulings. What are you doing otherwise?

Also, agree that PvP isn’t great. If one party is smart enough to focus fire (and take out the healer first), it can really come down to who wins initiative.

Also, depending on the level, there are lots of shenanigans besides death that can screw with characters in the long term: feeblemind, plane shift and flesh to stone come quickly to mind. Some are easier to deal with than others, but depending on party composition (the person who has greater restoration is the one who gets hit with feeblemind, for example) there can be really annoying consequences.

Well, if I separate the fights and take control of the "missing team" characters so I don't have people cursing at each other if they feel that their character was targeted or something like that. I would then have to manage the other team and try and make it an even fight. Maybe I'm o

I'm starting to understand more and more why it's not a good idea. I'm starting to think I should let them go at it one round and then introduce one of the BBEG and switch them to working together.....

Quote from Grushniak >>

Well, if I separate the fights and take control of the "missing team" characters so I don't have people cursing at each other if they feel that their character was targeted or something like that. I would then have to manage the other team and try and make it an even fight. Maybe I'm o

I'm starting to understand more and more why it's not a good idea. I'm starting to think I should let them go at it one round and then introduce one of the BBEG and switch them to working together.....

This will result in a combat that involves 8+ characters, and either a BBEG with 7 legendary actions and at least 600 hit points, and a tedious combat that involves the DM controlling as many characters as the PCs plus the monsters. Never use more than one friendly NPC in a combat unless it's vital.

Since you are running the opposing party in each campaign, just transfer the stats of the characters into monster stat blocks as follows:

• Martial classes - give them multiattack action, and up to 2 special features from the class
• Spellcasting classes - give them their 5 strongest spells plus one Reaction spell
• Then reduce their hit points and damage a bit so that they aren't equivalent power level