(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:
- 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.
- 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.
- 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?