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by Mike on 28 November 2022
A monster's challenge rating is a loose approximation of a monster's difficulty. Many factors not included in challenge ratings often affect the difficulty of a battle. Use the lazy encounter benchmark and dials of monster difficulty to build and run fun encounters and don't be afraid to run easy battles sometimes.
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The 5th edition of Dungeons & Dragons uses "challenge rating" (hereby referred to as CR) as a measure of the challenge of a monster. Every stat block for a monster or NPC has a challenge rating. Here's the description from the front pages of the Monster Manual.
A monster’s challenge rating tells you how great a threat the monster is, according to the encounter-building guidelines in chapter 3 of the Dungeon Master’s Guide. Those guidelines specify the numbers of adventurers of a certain level that should be able to defeat a monster of a particular challenge rating without suffering any deaths. An appropriately equipped and well-rested party of four adventurers should be able to defeat a monster that has a challenge rating equal to its level without suffering any deaths. For example, a party of four 3rd-level characters should find a monster with a challenge rating of 3 to be a worthy challenge, but not a deadly one.
Monsters that are significantly weaker than 1st-level characters have a challenge rating lower than 1. Monsters with a challenge rating of 0 are insignificant except in large numbers; those with no effective attacks are worth no experience points, while those that have attacks are worth 10 XP each.
Some monsters present a greater challenge than even a typical 20th-level party can handle. These monsters have a challenge rating of 21 or higher and are specifically designed to test player skill.
I've highlighted a couple of key sentences. The first highlighted sentence is the one we should pay the most attention to. A monster should be a worthy challenge — but not a deadly challenge — for four characters of an equal level to the CR of the monster.
That's not a terrible rule of thumb, but it's not terribly useful. Many factors go into whether a particular battle is going to be challenging beyond just the challenge rating of a monster and the levels of the characters. These factors include
What's important to note from the CR description above is that a single monster is roughly equivalent to four characters of an equal level to their challenge rating. That doesn't help us understand how multiple monsters work out, though. Which is why the Dungeon Master's Guide has it's crazy two-dial system for figuring out combat difficulty — a system both overly complicated and inaccurate in its results.
Challenge rating is a loose guide at best. Not only does monster difficulty vary significantly within a given challenge rating but monster difficulty also changes as challenge ratings go up. CR 1/2 creatures, for example, are much more deadly to 1st level characters than CR 5 monsters are for 10th level characters.
Challenge rating is an aggregate score of several statistics in a monster's stat block. A monster's challenge rating is the average of two measurements: offensive challenge and defensive challenge. Each of these two categories have various characteristics, measurements, and weights affecting their final calculation. You can find a full breakdown of these characteristics and measurements in the "Creating a Monster" section of chapter 9 in the Dungeon Master's Guide.
Sometimes these weighted characteristics dramatically change a monster's challenge rating but might not come into play in an actual battle. Other times, particular characteristics are overweighted, giving a monster a greater challenge rating than the actual threat it brings to a battle.
I often complain that high challenge monsters aren't nearly the threat that lower challenge monsters when compared to appropriately leveled characters. I argue that the characteristics of higher challenge monsters are weighed too heavily — high CR monsters need those abilities to challenge high level characters. An example is "legendary resistance" which counts as increasing the hit points of a monster but the whole reason a monster has "legendary resistance" is because it's going to be a huge target of "save or suck" spells. It needs those resistances because of the role legendary monsters play in the game. That's one example of many.
It's not important to break down every characteristic to see why a monster landed at the challenge rating it did. Instead, note the most important conclusion of this article:
Challenge rating is, at best, a loose approximation of the difficulty of a monster.
How do you make sure high CR monsters fight at their challenge rating? Bump up their damage.
Two online tools help calculate encounter difficulty using the math from the Dungeon Master's Guide: Kobold Plus Fight Club and the D&D Beyond Encounter Builder. Both use the DMG math which, as noted, isn't particularly accurate in a vacuum. I'd argue "hard" encounters by these calculations aren't actually hard above level 7 or so given what characters bring to the table.
If you're looking for easy measurements of combat challenge you can keep in your head, consider the lazy encounter benchmark. This benchmark doesn't break down "easy", "medium", "hard", or "deadly" levels. Instead, it focuses on identifying potentially deadly encounters. Encounters below that benchmark are easier and things above it are harder. Here's the benchmark:
An encounter might be deadly if the total of monster challenge ratings is greater than 1/4th of the total of character levels, or 1/2 if the characters are above 5th level.
These are loose measures at best. Due to all of the factors described earlier in this article, this comparison is only a loose gauge. Various circumstances and criteria change an encounter's difficulty dramatically.
High level characters have so many resources at their disposal that combat gets even less predictable. In the original Monster Manual description above I highlighted the section talking about CR 20+ monsters being significant challenges for 20th level characters. That's certainly not been my experience. I've watched high level characters eat through challenges far greater than a single CR 20 monster.
Returning to the main question, what does CR actually mean?
Challenge rating is a loose approximation of the difficulty of a particular monster compared to the level of the characters. Only when combining it with some encounter building math can we figure out its true relationship to the characters and those results are, at best, a loose approximation of encounter difficulty. Many factors go into the difficulty of a battle and thus it's up to each of us DMs to gauge each encounter and the potential difficulty it brings to the table.
What can you do with challenge ratings? Use the lazy encounter benchmark to gauge a potentially deadly encounter and use the dials of monster difficulty to tune monsters to suit the situation and pacing of the game.
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