Does the Vrock Spores ability stack? If so, does a single saving throw end both?

Question

Vrocks have a "Spores" action (with a recharge of 6) that releases a 15­-foot­-radius cloud of toxic spores:

Each creature in that area must succeed on a DC 14 Constitution saving throw or become poisoned. While poisoned in this way, a target takes 5 (1d10) poison damage at the start of each of its turns. A target can repeat the saving throw at the end of each of its turns.

If the vrock uses the ability a second time, and the victims still haven't made the saving throw from the first one, do they take 1d10 or 2d10 damage at the start of their next turn?

I think it's 2d10 RAW, but perhaps not intuitive.

And if so, do they then need to make two saving throws to end the two effects?

Answer 1

No, the spores will not stack.

In the DMG on page 252¹, "Combining Game Effects" it says:

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. (DMG 252)

Thus, a PC will only experience the effects one spore at a time no matter how many times they are hit with the ability.

This is also backed up in the PHB section on conditions which says:

If multiple effects impose the same condition on a creature, each instance of the condition has its own duration, but the condition's effects don't get worse. A creature either has a condition or doesn't. (PHB 240)

Since Spore inflicts the poisoned condition, it cannot be applied again to make the poisoning worse. In this case, there really is no duration so applying it again just does nothing.

So, no matter how many times you get hit, if you fail your save you take 1d10 damage at the start of each of your turns.

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^{1 - this was not present in early printing of the DMG and was added as errata which you can find here. Subsequent printings do include the new text.}

Answer 2

They don't stack.

As per Conditions, PHB p.240:

If multiple effects impose the same condition on a creature, each instance of the condition has its own duration, but the condition's effects don't get worse. A creature either has a condition or doesn't.

Vrock spores fall under that rule, as they impose the poisoned condition, like so:

1. The targets must pass a saving throw or become poisoned (a status effect).
2. While poisoned in this way, a target takes damage at the start of its turns.

The vrock poisons you, and you take damage on your turn while poisoned. But since you can't apply the same status effect twice, a vrock cannot poison you twice. You don't become more poisoned, you're just still poisoned.

A single saving throw will cure you of the poisoned condition, regardless of how many times you were hit by spores ability.

Answer 3

Designer Ruling

Jeremy Crawford tweeted:

[N]othing in the game that has the same name stacks. #DnD

That means that it would only be saving rolls and damage for only one use, but the duration would be that of the last the duration while any one of them is up. If someone succeeds their save and then another Vrock (or the same one) spreads spores again, the player would have to make another save roll, and potentially be pulled back into the mess. Overwise, a failed save means the PC gets 5 (1d10) no matter how many times the Vrock spreads the spores, and one save at the end of each round. Anything else would be very hard to track, and against designers intent and official ruling.