There already exist a few questions asking similar things about such scenarios, like the following:
- If a wildshaped druid somehow got Undead Fortitude, would this prevent them from reverting?
- Does Phoenix Spark overcome Disintegrate?
- Does casting Disintegrate on a polymorphed enemy still kill it after the 2018 errata?
- Does the Way of the Long Death monk's Mastery of Death feature protect against the Disintegrate spell?
- What happens if a sorcerer is hit with Disintegrate while he has turned into a potted plant?
What I am wondering is whether the wording differences between all of the following features means anything; how should these wording differences be interpreted/used? In particular, some features use the phrase "when you would be reduced to 0 hit points" while others use the phrase "when you are reduced to 0 hit points".
The first link above currently has an answer stating that the wording difference is important, and that it does result in differences between the features and rulings regarding them. Below are some example features:
If you drop to 0 hit points while you're raging and don't die outright, you can make a DC 10 Constitution saving throw. If you succeed, you drop to 1 hit point instead.
If damage reduces the creature to 0 hit points, it must make a Constitution saving throw [...] On a success, the creature drops to 1 hit point instead.
When you are reduced to 0 hit points but not killed outright, you can drop to 1 instead.
You automatically revert if you fall unconscious, drop to 0 hit points, or die.
When you are reduced to 0 hit points, you can expend 1 ki point (no action required) to have 1 hit point instead.
If the boar takes 7 damage or less that would reduce it to 0 hit points, it is reduced to 1 hit point instead.
The first time the target would drop to 0 hit points as a result of taking damage, the target instead drops to 1 hit point, and the spell ends.
Only the last two features actually use the phrasing "would drop" and "would reduce" instead of simply "are dropped" and "are reduced" (or similar). Does this mean that death ward and the Relentless feature act differently in terms of rulings to be made?
Is there a difference between "when you are reduced to 0 hit points" and "when you would be reduced to 0 hit points?"
I would like answers to assume that the wording choice of "if" vs "when" is irrelevant. These words (at least to me) seem to be used interchangeably throughout the rules with no difference in meaning, so they can be ignored here. Alternatively, if you feel they are different, that should be a separate question of its own.