Hi all. I've been trying to systematize homebrew monster creation, and I've been wondering whether there's a good way to assign proficiency to saving throws for monsters. Most monsters that aren't intelligent seem to have no save proficiencies, while others seem arbitrary. I'm not a big fan of assigning proficiency to the saving throw associated with the highest stats. What I've been doing is finding the character classes that most respresent the role of the monster, and using those save proficiencies: ie. a cult leader would have proficiency in Wisdom and Charisma as a warlock or cleric would.

What systems do you use?

There's a book out there called The Monsters Know What They're Doing, or something similar. It's a collection of that authors web posts, I think, so you might be able to find the stuff online anyway. I just searched: This Link

He breaks down the fighting tactics of monsters from the MM based on what stats they were given, plus any special abilities they might have. Might give you an idea for homebrew monsters if you read a couple articles.

Or maybe the history write-up for your homebrew gives you ideas after you stat it up? . For example, you make some brute monster with high Strength and Constitution, but you write up a history where the monsters mostly live near some wizard enclave, so they developed different saves to adapt to their enemy, like Intelligence or Charisma.

I've had that book in my Amazon cart for a while. May be time to actually get it.

I was thinking along those lines as well. For context, I have a group of angelic creatures I've been tinkering with for a few months, one of which is a celestial bear hybrid that specialized in divination magic. Although their stature gives them great strength, they wouldn't typically train to harness that strength in combat or otherwise, suggesting that a high Strength score doesn't necessarily imply proficiency in Strength saves. It's enough that their Strength saves would be high on account of their raw score.

On the other hand, the more combat-oriented celestials in this group may have proficiency with Strength, but would also have proficiency with Charisma saves, operating as a Paladin would, even though their Charisma score is nothing special.

Have you considered maybe specialized groups have special abilities?

For example, say that group has proficiency in Str and Cha saves, but since they mostly deal with evil magic users (or something) they've trained to have Advantage on Wis saves?

So they look like a "regular celestial" (breastplate and greatsword, or whatever), which makes me make an assumption about who they are (I assume they're a tank), and I try to think of a weakness I can exploit (I'd assume low Int, or Wis), only to find out this particular celestial is trained to fight idiots like me who judges books by their covers.