I'm DMing for a party of 6. In our next session, I'm planning on running four combat encounters. With such a large group, I've found that it usually takes an hour or two to get through a single battle. So I'm potentially looking at an 8-hour session!

However, I've also noticed that once my players have taken out most of the enemies in an encounter, the outcome of the battle is set in stone. The players will win, it's just a matter of time. Even so, it can take 10-20 minutes and multiple rounds around the table to finish lopping off those last few hit points. Skipping these rounds and saying the enemies are just dead doesn't quite work because the players will probably lose a few more hit points and spell slots/ability uses before the end of combat. I want to balance my dungeons on the attrition between consecutive fights.

How can I speed up these last few rounds of an encounter without letting my players keep all of the HP and spell slots they would have used had we played them out in full?

(I'm looking for answers other than making the enemies retreat. I can do that in a lot of situations, but I'd like other options as well. And sometimes, enemies will want to fight to the death no matter what.)

Estimate it

One rule that a lot of DMs forget is that not every single combat encounter—or more specifically, every single moment within combat—needs to be handled in the Combat-Initiative Abstraction. A group of level 5 characters facing off against a single CR 1/4 goblin doesn't need to open with Initiative, and similarly, if a group of characters are up against any encounter whose difficulty is trivial to surmount (or they've whittled an encounter down to this point), you shouldn't feel compelled to mechanically iterate through each moment of that combat. Just use a single d20 roll (maybe a contested ability check?) to determine how many hit points are used up.

Surrender!

It depends on what kinds of creatures the players are up against, but most NPC creatures possess a modicum of intelligence and sense of self-preservation. If they see that the fight has clearly gone south for them, it's reasonable for them to surrender or run away, eliding what would otherwise be the grueling remainder of the fight.

Like in the example above: instead of narrating that the level five characters mercilessly brutalize the goblin, maybe the goblin just immediately surrenders without putting up a fight—or hopefully the players didn't intend ill will towards the goblin in the first place!

There's direct precedent in some adventure modules for this as well. For example, in the Lost Mine of Phandelver adventure, the very first encounter in the module suggests this course of actions for the goblins the PCs encounter:

Four goblins are hiding in the woods, two on each side of the road. They wait until someone approaches the bodies and then attack.

This will likely be the first of many combat encounters in the adventure. Here are the steps you should follow to run it effectively:

• [...]




• When three goblins are defeated, the last goblin attempts to flee, heading for the goblin trail.

—Goblin Ambush, Lost Mines of Phandelver, D&D 5th Edition Starter Set

Having said that...

I do need to slightly challenge the premise of this question. It's one thing if you're only expecting players to lose a few more hit points to a lucky hit by their enemies, but if you're expecting players to still use up spell slots, that implies pretty strongly that the outcome of the fight is very much not set in stone. Even at high levels, a spellcaster would probably prefer to use their cantrips if they don't expect to need their spell slots.

So while the above advice is, in my opinion, a pretty good rule to follow, it should be tempered with the advice that if the players can be expected to expend expensive resources as part of their effort to end the conflict, it's probably too early to call it.

Offer bartering resources to solve encounters.

I once had an RP-table that wanted to try how a "real" dungeon feels like so I prepared a complicated dungeon with multiple complex traps, puzzles and several creature-encounters.

The whole dungeon was an attrition-based set-up of multiple dungeon layers. The group had a lot of fun solving puzzles and traps, but then there were the creature-encounters.

After three creature-encounters, it was absolutely clear that the group rather wanted to do their usual low creature-encounter play-style. So we decided to take a pause, it was time for food anyway, and we took that time to talk about how we could salvage the problem.

Should we delete the creature-encounters and destroy the careful attrition-balance? This was not an option as we still wanted that "real" dungeon experience.

So instead, we came up with a solution of trading resources for encounters. The group could decide once the initiative was rolled (after set-ups, sneaking around and surprise rounds) to trade spell slots, hp and ability use to "auto-solve" the creature-encounters.

We did this by bartering after the decision was made to solve an encounter by spending resources - I told them the creatures involved and their CRs. This turned out to be a more enjoyable and less grindy experience. I doubt that it works at tables that aren't in the mood to get silly and creative.

The trades worked like this: I present the creatures and the group meta-games solutions and offers me resources that they deem appropriate, I accept or demand more (never less). The mood was less serious and more playful an example:

For the enemy with invisibility, we offer you a pound of flour, and we
all should probably make a Dex-save and take half of the dust
explosion, that dmg is your call.

For the narrative, I improvised narrating the last actions of the encounter based on the resources spent.

So if your table is more into creative solutions and bartering, then a trade can save time and make the time spend on creature-encounters more enjoyable for your Rp-heavy group.

A few caveats, I can easily see this grow tedious in a rules lawyer heavy-group and only recommend this solution if it suits your table.

This bartering system also heavily relies on estimations and the willingness of your players to offer their resources, they may become more stingy if they feel like they have already solved the encounter. Especially after they realise the rest of the encounter which robs the mystery of hidden enemies etc. so be open about communicating your intentions clearly - that includes that you expect your group to actually offer resources even if the rest of the encounter seems trivial.

A few ideas I often implement that I picked up from various GMs and websites. Some of these involve retreating, but I'll list them anyways to be complete.

Most of these kick in (initiate, or are triggered) when either the enemy leader dies, or 1/2 of the enemy units (round up) are defeated. When one of those two happen:

1. All enemy units make a save (whatever you feel is fitting). If they fail they check, they surrender, flee, or die/vanish (whatever you feel is fitting for the NPC). Some NPCs (based on type or nature) won't make this check, but >2/3 will.




2. When there are less than 1/2 of the enemies left, enemies reduced to X% of their HP are instantly defeated. (Normally I go with 20%)




3. Damage-dealing critical hits instantly defeat "normal" enemies, no matter the remaining HP.

A last option I often use is grant an additional enemy killed per turn if the player gives a sufficiently good/entertaining (mostly: did the table enjoy it? They normally do) tale of how they killed the enemy.

"After a few more blows and cantrips, the defeated enemies lie dead at your feet. What do you want to do now?"

Once the narrative question of the scene has been answered the scene is over so transition to the next one. The narrative question in a combat is "Will the characters win?" - once its been done its no longer a combat - its mopping-up.