Do Life Drain attacks from wights stack?

Question

The wight has an attack called Life Drain:

Life Drain. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 5 (1d6 + 2) necrotic damage. The target must succeed on a DC 13 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

A humanoid slain by this attack rises 24 hours later as a zombie under the wight's control, unless the humanoid is restored to life or its body is destroyed. The wight can have no more than twelve zombies under its control at one time.

If the same wight hits a character with it multiple times, or a number of wights hit the same character with it, assuming the character fails their Constitution save each time, do the max HP reduction effects stack?

I know magical effects don't normally stack, but this isn't listed as being magical. Additionally, if it doesn't stack, I can't see how most characters could ever have their max HP reduced to 0.

Answer 1

Drain effects are intended to stack

As explored in detail in the accepted answer, there is a rule in the DMG according to which multiple ongoing effects from a feature with the same name do not stack. Different instances of the Life Drain ability come from a feature with the same name. So using a strict, technical reading of the rules, the Life Drain would not stack.

However, there is an analogous question in the Sage Advice Compendium, which provides official rulings on how to interpret rules, on the Strength Drain of the shadow:

Since game features of the same name don’t stack, does that mean a target can’t be affected by a shadow’s Strength Drain more than once between rests?
The intended function of Strength Drain is that it stacks with itself, as signaled by the fact that you die if your Strength is reduced to 0 by it.

Note that the answer does not say the drain as written does stack. It says the intended function is that the drain does stack. The authors are implicitly admitting that their rule, as written, does not work, but they tell you how it should be read to work. The same applies to the Life Drain of the wight, down to the justification that it says it can reduce the resource it affects (in this case, your hit point maximum) to zero.

Answer 2

Yes, it "stacks".

There is a ruling on combining game features, but that is only talking about ongoing continuous effects. i.e. the effect that is causing ongoing damage rather than the damage itself. Consider the example given there:

For example, if a target is ignited by a fire elemental’s Fire Form trait, the ongoing fire damage doesn’t increase if the burning target is subjected to that trait again.

As it states, this is talking about the ongoing effect (the ignition from the Fire Form trait, which you can only be affected by once even if affected by more than one fire element) and not the damage itself, which is obviously 'stacking' damage each round.

The wight's attack does not say this is an ongoing continuous effect. Like the damage itself, it is an instantaneous effect that reduces your max HP. To see it another way, there is no reason for it not to behave with the same logic/rules as ordinary HP damage (otherwise you could argue that HP damage doesn't 'stack' if you get hit by the same sword multiple times!).

The sentence in the wight's attack, strongly suggests this is the intent:

The target dies if this effect reduces its hit point maximum to 0.

Comparison with standard Hit Point and Damage Rules

Standard damage rules state:

Whenever a creature takes damage, that damage is subtracted from its hit points. The loss of hit points has no effect on a creature's capabilities until the creature drops to 0 hit points.

Again, this clearly doesn't last only while you are getting damaged. The source of the damage may be instantaneous or ongoing (damaging you each turn), but the damage, unfortunately, accumulates until you drop to 0 HP or until you get healed via some other effect or until you rest:

At the end of a long rest, a character regains all lost hit points

Answer 3

It looks like the answer is: No it doesn't stack

While this may be a magical effect, the combining of magical effects you are referencing refers to spells specifically.

Combining Magical Effects

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect-such as the highest bonus-from those castings applies while their durations overlap.

For example, if two clerics cast bless on the same target, that character gains the spell's benefit only once; he or she doesn't get to roll two bonus dice.

(Player's Handbook, page 205)

Bolded by me.

As you can see this rule is referencing spells.

However, there is also this errata to the DMG:

Different game features can affect a target at the same time. But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap. For example, if a target is ignited by a fire elemental’s Fire Form trait, the ongoing fire damage doesn’t increase if the burning target is subjected to that trait again. Game features include spells, class features, feats, racial traits, monster abilities, and magic items. See the related rule in the “Combining Magical Effects” section of chapter 10 in the Player’s Handbook.

The Life Drain ability which wights possess is not a spell, but rather a creature's ability. But apparently in recent errata it doesn't stack.