dungeons and dragons – Does D&D have any sort of interaction that affects constitution saves similar to how Evasion affects Dexterity saves?

D&D 3.5e — “Mettle”

In D&D 3.5e, evasion allowed someone to take no damage on a successful Reflex save against something that usually had halved damage on a successful save. This feature was originally available to monks and rogues, and became available to other classes via supplemental content.

Later in the same edition, additional classes were introduced that had a feature called “mettle,” which worked the same way, except instead of Reflex saves, it worked on both Fortitude and Will saves.

Note that D&D 3.5e only had these three saving throw types—Fortitude based on Constitution, Reflex based on Dexterity, and Will based on Wisdom. There were no saving throws associated with Strength, Intelligence, or Charisma. (These associations were only defaults, however, so special features could and occasionally did change the ability score associated with a given type of save.)

Mettle covered both Fortitude and Will because it was (and, I believe, continues to be, in 5e) relatively rare for those types of saving throws to still have some reduced effect on a successful save. Usually, those kinds of saves just negated whatever the effect was entirely.

To my knowledge, there was no “half-mettle” feature that covered only Fortitude saving throws.

D&D 4e — “Mettle” again

In D&D 4e, we still have Fortitude, Reflex, and Will, but now they are no longer saving throws, they are “defenses” and work the same way that AC does—certain powers had you roll your attack against these defenses instead of AC. (Saving throws were an entirely separate mechanic and there was only the one type, “saving throw.”) Also, Fortitude was based on Strength or Constitution, Reflex was based on Dexterity or Intelligence, and Will was based on Wisdom or Charisma, whichever was higher out of each pair.

But evasion and mettle remained effectively the same—evasion caused attacks that targeted your Reflex to do nothing on a miss, even if they usually did something on a miss, and mettle did likewise for attacks that targeted Fortitude or Will.

D&D 5e — none, I believe

As far as I can tell, D&D 5e doesn’t have mettle, or anything similar to it. It might be hard to make in 5e, since Dexterity remains the saving throw associated most strongly with partial or reduced effect on a successful save, but “everything but Dexterity” is now five separate saving throws, instead of just two, which makes having mettle cover all of those seem a fair bit more imbalanced. At any rate, Wizards of the Coast has yet to cover it in their publications.