How can I very quickly summarize a series of easy combats?

Question

(Similar to this question, but for 5e and with slightly different requirements.)

I have a group of players who are in an area where there are two opposing factions they're planning to pit against each other. Now, the overall outcome of the battle is all but inevitable (Hoard of the Dragon Queen spoilers):

The PC's have infiltrated Castle Naerytar, posing as cultists with Snapjaw's help. They plan to assassinate Spattergoo - if they're successful, most bullywugs will flee, leaving only a few of the braver ones, the giant frogs in the basement, and the cultists to oppose the PC's, 40-odd lizardfolk in and around the castle, and the giant lizards.

So I don't need to simulate the entire battle. But my players are likely to run into several groups of half a dozen relatively weak enemies before dealing with their commander. I want to rough them up a bit before the boss fight - but it's a large party, and I don't want to play out a bunch of easy fights; my players (who are enough focused on the narrative that we're thinking about a different game, like Dungeon World, next time) will get sick of it before the boss fight even starts.

How can I resolve a fight using only a few rolls? The top answer from the linked question looks pretty good, but is still more detailed than what I'm after. Within about 30 seconds, I want to say "OK, you've killed or driven off everyone from this bunch, and PC 1 and PC 2 took $DAMAGE. You continue towards the tower..."

Ideally, I'd be able to take these factors into account:

• Initiative (at least at the group level)
• Attack bonus and average damage of enemies
• Total HP and average AC of enemies
• AC of each PC (i.e. less armored PC's should be more likely to take more damage than higher-armored ones)
• Whether or not the PC's elect to use a spell in combat

I don't mind doing some calculations in advance ("OK, based on this formula, a group of 4 regular cultists and 2 dragonclaws has a combat factor of 5"), as long as it's quick in play.

To give you an idea of the level of complexity I'm looking for, what I'm toying with so far is this:

1. Everybody rolls initiative, with the enemies only making a single roll. If more than half the PC's go before their enemies, figure they pretty much charge, skewer, escape unscathed, and move on.
2. Ask, in initiative order, if the PCs have any clever ideas or spells they want to use. If they do, and it's sufficiently impressive, the fight also ends without the party taking any damage.
3. Otherwise, everybody rolls damage against themselves - maybe 1d6-1 for AC20, 2d6-2 for AC17, 3d6-3 for AC15, something like that.

This would probably be OK, but each fight is either no damage or a lot, and I'd prefer "a bit of damage per fight" to be a more likely outcome. Also, I'd need to customize the damage dice in step 3 for each enemy group, and I'm not sure the best way to do that.

Has anyone attempted to abstract d20 combat in this way - basically saying "Statistically, combining all the rolls you'd make, this is the average outcome for a fight like this"? Maybe something making use of calculations for average damage per round?

Answer 1

Suggest a resolution for the combat but let the players decide if they accept it.

If not, make a new suggestion or fight it out.

For example, based on your best judgment and gut feeling, you guess that the enemy would get three swings at the primary fighter characters and one at someone else. So you suggest to players: rather than play this out in detail, how about you kill them, each spellcaster uses one 1st level spell, and I get to make three attack rolls at the frontline fighter and one at a random party member. Is this okay?

Then let the players narrate how it goes, if they are so inclined.

Obviously, do not use this when there are significant hidden factors at play, non-standard enemies, a complicated combat with three or more sides, etc., as those are usually interesting to play out and hard to estimate with any reliability.

Note that this is an inherently fair solution, in that the players can always decline. This is also a modular solution: "How about you kill all the melee opponents while the goblins are shooting at you; I get two shots at everyone and the grunts get four swings total divided as you want, and all the grunts are down afterwards?"

Answer 2

Make It Quick Or Make It Interesting

What you're aiming for appears to be in an awkward space between relevant gameplay and pure narrative. Having a series of Initiative rolls and one-time questions if/how they want to influence the outcome to determine how fights will go, will not be satisfying for your players - luck and a "switch" they can try to flip on momentary information do not convey agency or present any interesting decisions. So you'll have to decide if it's a scene that's worth your time and then make it good, or if it's really just a transition between interesting scenes and then make it quick.

This argument is based on the AngryGM's defintion of an encounter; more precisely, this part of it: without points at which your players can make decisions to influence things, an encounter is not worth being kept around and should be brought to conclusion quickly.

Make It Quick

Therefore, if your players aren't interested in that kind of fighting scenes, just have whatever attrition you want them to suffer prepared and narrate how they fight their way through these smaller groups. Make sure to include the occassional cut or bruise and at the end declare what damage they suffered. You could ask them whether or not they want to expend resources for these fights, explaining that doing so will increase their chances of getting through with little harm done - have a second outcome prepared, including reduced attrition and some resources spent. If they come up with something during your narration, allow it and depending on how good an idea it is adjust the attrition accordingly. If they're eager, let them take over part of the talking and describe for themselves how they handle their enemies.

No need to get fancy with maths and rolls to drag the whole thing out and make it complicated for the sake of "precision" and some pseudo-influence on the outcome. All the values you mentioned, minus the Initiative are under your control anyway. Just make sure beforehand that your group is OK with that kind of low player agency scene.

Make It Interesting

Your other option is to flesh it out and make it a worthwhile experience. But this will take more work, will definitely go way beyond your 30-second mark and might just end up being a full-fledged fight anyway. To avoid the latter, you can replace the regular combat by narrative combat. You talk through whatever tactical approaches your players can come up with, without actually rolling dice, and you adjudicate how well they fare. You need to have a very firm mental grasp of the situation though, very fleshed out environments and the ability to convey it to your players to make that work. That's because you'll have to offer cues and hooks for narrative options (aka decisions) to make up for the lack of mechanical ones they usually have in combat.

Answer 3

I wholeheartedly concur with xNGTMx's answer. The best way to solve this is to have your players sign over some agency to you, and trust that you will judiciously determine the outcome of the fight without making them spent an hour on each fight. Heck, play out all the potential fights yourself and just record the net effect on hp and limited resources for each fight, and record them. Then when your party encounters guard group 3, you just narrate the fight with your players, and tell them at the end that the Barbarian took 5 points of damage and the wizard cast one 1st level spell. But if you insist on playing out the encounters at the table, here are some tips that you can use:

Static initiative

Have all of your players roll initiative​ once at the start of the session, and carry that initiative with them for the rest of the session (I did this in the dungeon at the end of LMoP and it went great, although if I were to do it again, I would have them roll 1d10+6+mods or 1d8+7+mods instead of 1d20+mods, to reduce the effects of fluke dice since they are going to be stuck with that initiative order for the entire session).

Then roll one initiative per 5 monsters (to avoid making things too swingy if they roll high or low) and put them where they belong in the order. Or use the static 10+mods to make things even quicker.

Average damage / # of hits to kill

Rather than keep track of hit points, figure out your players average for when they aren't expending resources (normal sword swings, cantrips, etc...). Compare this to the monster type(s) they are fighting and determine the average number of hits it will take to kill them. Now only keep track of the number of hits. Crits are worth 1 extra. Expending a resource can either be worth 0.5 or 1 extra, depending on how powerful it is (1st level spell vs cantrip is definitely +1 hit, a fighters battle master maneuver is probably only +0.5). AoE spells probably do 1-2 hits depending on the level, but hit everyone in their area.

The fight has now been reduced to a series of to-hit rolls. Encourage your players​ to set a default strategy, and let you enact that while they roll dice, and correct you on any applications, or where they want to act differently.

Mxyzplk's quickie mass combat rules

You already linked to mxyzplk's 3e/3.5e homebrew rules for quick mass combat. I would try to transfer them to 5e, but I am not familiar with 3/3.5 to be able to make that comparison. But they will not break the game even if you play them as is. You could simulate a few battles yourself, and compare mxyzplk's rules as applied to 5e with a full played out combat if you really care to get the numbers right but it sounds like you and your group probably don't care.

Answer 4

Don't change the rules

While I see your desire to somehow speed combat along, I think changing the rules to fit this particular situation isn't necessarily the best course of action. Your assumptions might be correct (lowered AC PCs will take more damage) but you fail to account for multiple PCs being cleverer than just one DM (my lower AC character hides until she see's a sneak attack opportunity). And now you're trying to introduce rules on the PCs that they havn't had time to digest, and decide if they would rather use those quick fight rules or play out the encounters.

Make encounters meaningful

If the PCs grossly over power a typical patrol of minions, and they can control the situation, then just tell the PCs that they've routed their enemies, and proceeded to the next area. If you have lots of these, but still want to rough the PCs up, then make one or two (instead of 4 or 5) encounters with enough enemies to pose an actual challenge. This will give the PCs some quick time to be awesome and dispatch lots of low-powered monsters. Feel free to use techniques like 1hp for minions and tricks for Lieutenant-level monsters. Also, you can present opportunities for the PCs to use up their resources like short/long-rest abilities, spells, and items with charges.

You won't take away agency

Even if you do your best to control the PCs and have them take damage and expend resources in smart and efficient ways, you'll still be taking away the choices that make role-playing what it is. Even if the best choice for a given encounter was to use the last charge on the firebolt wand, maybe the PC was really saving that for the next wax golem and he had some birthday-candle joke prepared. Or maybe you, being one DM, didn't consider that another PC would gladly use up their long rest abilities to avoid taking even a single point of damage, even if that means being unprepared for the boss fight. Let the PCs make their beds, and sleep in it. (Is that a saying?)

Change the situation instead

If the current module is set up in a way that does not make sense for your party to play and have fun, change it so that it is fun. Honestly, the time it takes to set up a scene and have all the PCs understand the opponents and terrain and all the things can take enough time that, yes, lots of little battles can slow down the game. So don't do that. Do medium-sized battles that can actually be fun and engaging and force the PCs to think and find the best way to deal with enemies, even if just charging into battle would be a pretty easy task.