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by Mike on 2 March 2020
Lazy Encounter Benchmark: An encounter may be deadly if the sum total of monster CRs is greater than one quarter of the sum total of character levels, or half the sum of character levels if the characters are above 4th level.
This lazy encounter benchmark abstracts the math behind encounter building and monster challenge ratings to help you gauge whether your story-based combat encounter may end up deadly.
This lazy encounter benchmark uses two steps and all of it can be done without any online tool or referenced table.
The second step requires some work to understand but once you see the examples it should hopefully click. 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 the situation. That's step one. We didn't yet worry about "balancing" this encounter, it came from what makes sense given the situation.
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 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 given 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 encounter building benchmark has numerous advantages over others.
First, it scales well for any number of characters. Since you're adding together all of the character levels, it works the same if you have three characters or six. We don't need to jump to another column in a table; we just add it all together.
Second, it scales up and down the range of challenge levels. If we have five 12th level characters (a deadly total CR benchmark of 30) we can use the same benchmark for CR 1 ghouls (more than 30 might be deadly), CR 9 fire giants (more than three might be deadly), or any mix of high and low CR creatures. We just add together all of the CRs of all of the monsters we're considering and see if its higher than the threshold.
Third, we can do it quickly in our head. As long as you can remember an encounter may be deadly if the sum total of monster challenge ratings is greater than one quarter of the sum total of character levels, or one half of character levels if the characters are above 4th level you have what you need. Some quick math gives you the answer. You can write this threshold down in your prep notes while preparing for your game just to have it handy.
This benchmark works when used with a few assumptions.
First, it assumes you don't have more than one legendary monster in a battle. The math would still work out but battles with multiple legendary monsters are going to be terrible to run. Use just one legendary monster in a battle.
Second, it assumes you're using more than one monster in a battle. This benchmark doesn't work particularly well to benchmark a single foe versus the characters. Instead, it works well for groups of monsters with any range of CRs.
Third, instead of using it as an encounter budget, 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.
Any DM who has played this game long enough recognizes that any system for measuring combat challenge in D&D 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 easy-to-implement benchmark to give you a rough idea if an encounter may be deadly.
Guidelines and tools like this one help us stay fast and flexible while running our game. They give us the tools we need to improvise as our games go off in directions we didn't expect. Keep this lazy encounter benchmark in your brain-based DM toolkit and use it to help you run the most fun encounters you can.
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