[RPG] Determining DCs for monster abilities


I am working on a homebrew monster and reading the Dungeon Master's Guide p. 278 states I can

Use the Table. You can start with the monster's expected challenge rating and use the Monster Statistics by Challenge Rating table to determine an
appropriate save DC for any effect that requires a target to make a saving throw.

Calculate the DCs. Alternatively, you can calculate a monster's save DCs as follows: 8 + the monster's proficiency bonus + the monster's relevant ability
modifier. You choose the ability that best applies. For example, if the effect is a poison, the relevant ability is probably the monster's Constitution. If
the effect is similar to that of a spell, the relevant ability might be the monster's Intelligence, Wisdom, or Charisma.

Don't worry if the save DCs aren't matching up with
the expected challenge rating for the monster. Other
factors can affect a monster's challenge rating, as
shown in later steps, and you can always adjust the sa –
DCs later on.

So let's say I have a monster CR 17 with a 30 con score, and I believe the con score should be used for the ability. Calculating the save the DC would give me 8+6(proficiency)+10(con)=DC24. Alternatively I can simply use the table which gives a DC of 19.

Do I just get to pick whichever one best suits my monster??

Best Answer

Yes, you can choose as you like.

The advice given on how to create new monsters in the DMG is a set of guidelines to help you get in the right ballpark, not hard-and-fast rules about how all creatures must work. You can choose whatever values you want based on how challenging you're trying to make the creature.

Most of the time (but not always) in the published material, the DCs for abilities are derived using the 8 + Proficiency + Relevant Modifier formula, so for consistency's sake sticking to that formula is neatest. I think the DC values as given on the Challenge Rating table are mainly intended for putting things together very quickly so they're roughly acceptable, and they look like values you'd get if you were creating a creature with a reasonably good, but not exceptional, relevant ability score modifier. In your specific case, you're making a monster with a truly exceptional ability score, so it's not surprising that it looks very different to the quick approximation guideline.

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