[RPG] Is the Spirit Troll unable to be knocked out unless it doesn’t regenerate

If we assume that all spells and items at your disposal restore your health by regaining hit points, and we also assume that all the damage dealt to our hypothetical character was dealt by the Sword of Wounding, it would seem that the character is eternally stuck at 0 HP.

However, let us turn to the "Recuperating" downtime activity listed on page 187 of the PHB (emphasis mine):

You can use downtime between adventures to recover from debilitating injury, disease, or poison.

After three days of downtime spent recuperating, you can make a DC 15 Constitution saving throw. On a successful save, you can choose one of the following results:

• End one effect on you that prevents you from regaining hit points.
• For the next 24 hours, gain advantage on saving throws against one disease or poison currently affecting you.

So, after 3 days you can make a DC 15 Con save to try and remove the effect of the Sword of Wounding from your character. If you fail, you can try again in another 3 days, provided that your unconscious body is actually allowed to have downtime to recuperate (i.e. left to rest somewhere in a bed, while the rest of the party does their own downtime activities). Once you have made the save, you are both:

• stable at 0 HP, and
• able to regain hit points again, meaning that in 1d4 hours you will be back up with 1 hit point (or sooner with potentially more HP if you receive healing).

The rules as written are ambiguous - and so it's up to the DM's ruling (and designer clarification has gone both ways)

Unfortunately, it's not clear exactly how these rules interact. The troll has an ability which apparently specifies the only circumstances in which a troll dies, and these spells can cause creatures to die instantly; both are exceptions to the normal rules about how things can die, so the principle that "specific beats general" guides us in trying to resolve the conflict, but judging which of the two features is more specific seems subjective and ambiguous.

If you interpret the spell's rules as being more specific than troll regeneration, the troll dies; and since it is dead, regeneration becomes meaningless. If you interpret the troll's regeneration as being more specific than the spell, it precludes the death from happening despite the spell's effect.

Purely RAW ruling, on specific-beats-general principles, I would personally read the troll's ability as more specific than the spell; the spells can, after all, be used on many different kinds of creatures by many different casters, but a troll's regeneration is only ever about trolls, so it is necessarily much more limited in scope and therefore takes precedence over the rules of the spells.

JC says the troll dies

Official D&D 5e rules guru Jeremy Crawford weighed in when Rubiksmoose asked him about this issue on twitter:

Rubiksmoose: Trolls say that they die "only if it starts its turn with 0 hit points and doesn't regenerate". Does that mean they cannot be killed by power word kill/divine word? How about Disintegration?

Jeremy Crawford: If you're affected by the power word kill spell, it doesn't reduce your hit points to 0. It kills you. It thereby bypasses features that rely on you having 0 hit points. The disintegrate spell does reduce hit points, but if it reduces you to 0, you're dusted.

In this case he's just repeated previously given clarification that effects which state creatures are killed or die do not function by reducing the target's HP to 0, they just kill the target directly. This fails to address the actual cause of the ambiguity, so we can't really take it as a clarification of the rules as written.

The response in context implies that Crawford believed that this aspect of the troll's regeneration ability is only meant to stop the troll dying due to normal hit point damage (as a "feature that relies on you having 0 hit points"), not prevent any other effect which reasonably causes death.

And then JC says the troll doesn't die

When asked a very similar question on a later podcast, about whether or not the instant death (massive damage) rule could kill a troll, he suggested that it should not:

Jeremy Crawford: So if we're gonna use the troll as the example, here's what we're told: the troll regains 10 hit points at the start of its turn; if the troll takes acid or fire damage this trait doesn't function at the start of the troll's next turn; the troll dies only if it starts its turn with zero hit points and doesn't regenerate.

So in D&D the specific beats the general, and the massive damage rule is a general rule, and here we have the specific troll. But let's also look at the massive damage rule, because sometimes a general rule in the way we might think it does if we're just going off our memory of it...

[... looks up rules, reminisces about killing player characters ...]

So looking again at the instant death rule, the troll's exception overrides the general rule.

Bart Carroll: So it'll be smushed, but it will reform...

JC: It'll regenerate, yep, and that is part of the horror of the troll.

Instant death by massive damage doesn't kill you by dropping your hit points to zero; it just says you die. Dropping your HP to zero is a necessary precondition for this rule to apply, but the statement that "you die" isn't any more qualified than the effect of Power Word Kill. Coming back to it later, JC seems to have taken a more literal reading of the troll's regeneration ability and ruled that it really does only die if it meets the requirements specified by its regeneration ability.

It seems plausible that if he'd been asked specifically about trolls and Power Word Kill again, he might have ruled differently, depending on whether he thought the spell was more specific than the troll's trait. He does preface the judgement by explaining how loathe he is to make rulings about general hypotheticals, because D&D isn't a coherent rules system, and would probably argue if challenged that this ruling was specifically about instant death and trolls, whereas the previous was about Power Word Kill/Disintegrate and trolls, so they don't conflict at all.