It is known that occasionally questions will pop up that are about attempts to optimize a character's damage output (sometimes shorthanded as DPR, or Damage-per-Round), and veterans of this game know that which Armor Class values used to perform these optimizations can have pretty significant impacts on how you optimize for damage.
In the past, I've been using what I thought was a pretty good "Standard Array" for Armor Class values to test against: AC0, AC14, AC16, AC18, AC20, AC26, for the purpose of covering the following cases:
- AC0: Absolute "Ideal Scenario" gameplay, where bonuses are stacked high enough or creatures are vulnerable enough that their Armor Class is irrelevant
- AC14-20: Commonplace "Regular Play" scenarios, representing average-case damage output
- AC26: In officially published books, AC26 is greater than any Armor Class that any creature has; even the mightly Terrasque has an Armor Class of 25 in 5th Edition D&D
I'd also backed this with the context of the Dungeon Master's Guide, which in its table (page 274) describing guideline Armor Class values for custom creatures, it never goes below 13. So I've been operating under the premise that it's not realistic to perform DPR calculations against creatures that have an Armor Class of 13 or lower.
However, doing more research into how Statblocks are allocated in the Monster Manual and other supplemental books, I'm beginning to question this assumption. For example, despite AC13 being listed as a nominal minimum for even creatures as low as CR1/4 in the Dungeon Master's Guide, there are lots of creatures whose AC is well below 13, even for significant Challenge Ratings. In fact, nearly a third (369/1205) of the creatures found in officially published 5th edition materials have Armor Classes below 13, and even if you exclude the CR<1 creatures from that list, more than 10% of all creatures still have Armor Class values of 13 or lower. This list also includes relatively high CR creatures like the Corpse Flower, Giant Ape, Tyrannosaurus Rex, and other high CR creatures that have an Armor Class of 13 or lower.
My sense from seeing these statblocks is that while the 14-20 range might be accurate for some adventures and DMs, it may not be accurate for others, depending on what kinds of creatures are pulled from the manual to use in encounters.
Of course, I could just span the entire range from [5,25] to capture every single Armor Class that shows up in published 5th edition materials, but tables constructed with 21 columns of Armor Class values are unwieldy and difficult to read. So in an ideal world, I don't think I want to represent more than 6 or 7 distinct Armor Class values.
So I'd like to solicit some feedback: what would constitute a good array of Armor Class values to use in the future to try to represent the important use cases, if the use cases are:
- Creatures whose Armor Class is trivially low
- Creatures whose Armor Class is common and typical for a 5th Edition campaign
- Creatures whose Armor Class is uncommonly high for a 5th Edition campaign
- Creatures that constitute "Boss Monsters" with uniquely high Armor Classes