Every Dungeons & Dragons player experiences a battle that drags near the end, when the monsters have spent their best attacks and lack the numbers to threaten the PCs. As a dungeon master, I want to cut to the next scene, but thanks to focused fire, the remaining monsters stand near full health. Players won’t spend any resources on a fight that seems won, so they chip away with cantrips and basic attacks. The battle wears on.
Plan an out
The best combat encounters feature an objective different from kill all the monsters. PCs attempt to stop a ritual, defend a wall, close a dark portal, destroy an artifact, steal the brain in the jar, or accomplish some other task. Often, completing the objective ends the battle. Either the PCs escape or the summoned/dominated/animated defenders stop fighting.
In scenes where the players can win by slaying the necromancer or summoner who controls all the monsters, make sure the mastermind makes a difficult target. A typical dark lord won’t last a round fighting toe-to-toe with a rogue and barbarian. See The evil wizard’s guide to defense against murderous treasure hunters.
Dave “The Game” Chalker wrote more about The Combat Out.
Alternate goals make engaging combat encounters, but not every battle can turn on one.
Call the fight
When a winner becomes obvious, some DMs recommend calling the fight. Just sweep the monsters off the map. This fix seems tempting, but too many players hate the practice.
As a DM, you know more about the monsters’ conditions than the players. You may see an obvious win, while the players still feel tension.
Even when everyone sees the inevitable, your intervention jars the players out of their immersion in the game world. It leaves players feeling robbed of a victory they earned.
Only call a fight when a convention slot or other limit brings a severe time crunch—when you must move on or risk leaving an adventure unfinished. If you do call a fight, use narration to ease players out of the scene and give some sense of victory. Describe the characters’ final strikes—or invite the players to tell the tale.
Let monsters flee or surrender
Some argue that monsters would possess a sense of self preservation. That in the face of death, they would flee or surrender. I used to agree, but then I learned that bloodthirsty treasure hunters never show mercy.
Having monsters flee or surrender seems like a quick way to end a battle, but neither tactic saves time. PCs always pursue fleeing monsters, resulting in a chase. Only have monsters flee when you want a chase, or when the PCs simply cannot follow.
Surrender leads to a ugly interrogation scene followed by the dreary dispute over killing helpless captives. Finally, during the paladin’s bathroom break, the rogue murders the prisoners. (If you have never run these scenes, welcome first-time dungeon master!)
Sometimes, a surrender can lead to an interesting role-playing scene, or a real dilemma. Usually this requires foes who can (a) trade for their lives or (b) offer a good reason they should be freed. Nonetheless, surrender never saves time.
With either a chase or a surrender, you spend 30 minutes to save 5.
I suspect that in the monster community, word has spread about murderous treasure hunters and their rogues and paladins. Better to fall in battle than to die on your knees or with a knife in your back.
Turn monsters into minions
You can bring a fight to a quick end by silently deciding that all the monsters stand at only 1 hit point. The next hit kills. I’ve done it, but I never feel proud of it. I like a game where the players’ actions and the dice seem to decide the PCs fate. Even in a battle that seems won, if the players notice my meddling, they lose some sense that they control their destiny.
Still, as battles wane, when a blow nearly slays a monster, I may round the damage up to dead.
Near the end of a battle, typically only one type of monster remains. These survivors all act on the same initiative count, then all the players act. This situation permits my favorite way to close a battle: everyone roll at once. By now, the outcome has been decided, so no one would waste a spell slot. No player’s action requires my full attention. I announce the monsters’ armor class and invite everyone to roll their attacks and damage at once. If you need to move, just do it. Then I call out names and tally damage. In the time usually spent on one turn, all the players act. During these fast forwards, I used to ignore initiative and go around the table, having players call off their damage totals. But I learned that some players care about earning the kill, if only for the glory. So now I call names in initiative order.