by Mike Shea on 2 March 2020
Simplifying the process of building combat encounters has been a focus of Sly Flourish since the fifth edition of Dungeons & Dragons has come out. Along with running combat in the theater of the mind and running lots of monsters in combat, its an area we've tinkered often.
Previous guidelines for easier encounter building have worked well. I even released a free copy of the encounter building rules from the Lazy DM's Workbook to help DMs build combat encounters. That chart is solid, accurate, and mirrors the math found in the Dungeon Master's Guide and Xanathar's Guide to Everything.
Today we're going to try to simplify it even further. This new lazy encounter benchmark further abstracts some of the math behind encounter building and monster challenge ratings but it works well to help us build story-based combat encounters and gauge whether such encounters may end up deadly.
Best of all, this lazy encounter benchmark has only two steps and all of it can be done in your head without any online tool or referenced table.
Here's the Lazy encounter benchmark in two steps:
The second part requires some work to understand but once you see the examples it should hopefully click for you. Once it does, you can keep this guideline in your head and use it as a gauge to determine if encounters are edging into deadly.
Let's say we have four 3rd level characters and they stumble on a warband of ten orcs. That's our simple situation. That's step one.
Step 2. Is this encounter deadly?
We start by summing up all of the orcs' challenge ratings (1/2 each). This gives us 5. Next we sum up all the character levels which gives us 12. Since the characters are below 5th level, we divide the sum of character levels by four which gives us 3.
Since 3 (one quarter of the summed character levels) is less than 5 (the sum total of monster CRs), this is potentially a deadly encounter.
We have some options here. We can simply reduce the number of orcs from ten to six. The sum total of monster CRs (3) now matches the sum total of character levels (also 3). This is likely a hard fight but maybe not deadly.
We may instead decide to stick with the ten orcs but spread them out into multiple groups. Four of the orcs may wander away from the camp to hunt or might split up in two groups of two to guard the camp.
The story still drives the encounter but our benchmark tells us that in a certain situation, like facing off against ten orcs all at once, it may be deadly.
Let's say we're running the adventure The Styes from Ghosts of Saltmarsh. The villain in the Styes is a particularly nasty aboleth. Aboleths use chuuls as their personal bodyguards so our aboleth will have some chuuls hanging around. The aboleth has also been slowly converting the people of the Styes into sea spawns so some of them are hanging around too.
When the characters get into the aboleth's sanctum, it's likely to have some chuuls guarding it and some sea spawn lurking around. Let's say two chuuls and four sea spawns.
That's step 1. That's the current story. We didn't do any math yet. We just followed the story that the characters are about to face an aboleth and the aboleth has chuuls and sea spawn hanging around.
Now let's determine if this encounter is deadly. We start by adding up all of our monster CRs. The aboleth is CR 10. The two chuuls are CR 4 each. The four sea spawn are CR 1 each. That's a total of 22.
Let's say we have five 7th level characters. We sum all their levels together to 35. We half this number (rounding down) because they're 7th level. If they were 4th level we'd quarter it instead. Half of 35 rounded down is 17. That's lower than the 22 we calculated for the monsters. Thus it's a potentially deadly encounter.
But we like our story so we'll keep the sea spawn. They'll be mostly servants of the aboleth, non-combatants unless the aboleth is threatened. Then they'll protect the aboleth as a second line of defense.
Knowing that this encounter edges over into deadly means we can be ready for it when we run our game. We can adjust hit points, lowering them for the chuuls if things go too badly. We can keep the sea spawn as non-combatants. If we end up with more characters we can add more monsters and recompute.
This simplified calculation to determine deadliness doesn't hold up when you build theoretical encounters against single powerful foes. Six 8th level characters (a CR budget of 24) typically can't face and defeat a single CR 24 ancient red dragon. On the other hand, perhaps they could actually defeat such a foe; I've seen groups pull off greater feats; but I wouldn't expect it to go well.
Instead of theorycrafting encounters, always start with step 1. First, choose the monsters that make sense for the current situation and then use the benchmark to see if that situation is going to be deadly. Ridiculous encounters might actually work if you force them into the math but they're still ridiculous and you'll know it when you see it.
Any DM who has played this game long enough recognizes that any system for measuring combat challenge is imperfect. Many variables change the difficulty of an encounter including particular character builds, group synergy, environmental effects, player experience, magic items, particular spells or abilities, and so on. This simple benchmark isn't intended to be a perfect gauge. It's a loose benchmark that's easy to implement to give us a rough gauge of potential combat challenge.
We keep such simple guidelines in our head for one big reason, to stay fast and flexible while running our games. When we have loose guidelines instead of multiple pages of instructions and a bunch of charts we can improvise as the story changes in front of us. It's powerful magic.
Keep this lazy encounter benchmark in your brain-based DM toolkit and use it to help you run the most fun encounters you can.