To Kill a Vampire in Mist Form

Question

There are two different cases for a Vampire being in Mist Form.

1. By volition: (Shapechanger ability)
2. Via combat reduction to 0 hit points. (Misty Escape)

Shapechanger. If the vampire isn’t in sunlight or running water, it can use its action to polymorph into a Tiny bat or a Medium cloud of mist, or back into its true form.

Misty Escape. When it drops to 0 hit points outside its resting place, the vampire transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious, provided that it isn’t in sunlight or running water

While it has 0 hit points in mist form, it can’t revert to its vampire form, and it must reach its resting place within 2 hours or be destroyed.

My concern is that the Vampire being at 0 in mist form may be an edge case for the general 0 HP further damage rule.

Here is my line of thought. The Vampire takes on mist form and stays at zero hit points. It is "in transit" in mist form to its lair at a movement rate of 20.

MM p. 297

While in mist form, the vampire can’t take any actions, speak, or manipulate objects. It is weightless, has a flying speed of 20 feet, can hover ... if air can pass through a space, the mist can do so without squeezing, and it can’t pass through water. It has advantage on Strength, Dexterity, and Constitution saving throws, and it is immune to all nonmagical damage, except the damage it takes from sunlight.

This leads me to believe that a party can destroy the Vampire without having to wait for two hours or put a stake into its heart when it arrives at its coffin/lair. The method is that the vampire in mist for can be destroyed by continuing to do magical damage until it fails 3 death saves.

Rule loophole: death saves may only be for characters, not monsters. It is unclear if monsters are utterly exempt from that provision, even though PHB 198 says.

the DM might have them fall unconscious and follow the same rules as player characters

As I read the description, the Vampire regeneration of 20 HP per round is constrained to its humanoid form, bat form, or it's misty form if it changed into that form by volition and while it has at least 1 HP.

A Cleric can typically move at 30, a Vampire's mist can move at 20. My instinct is that a party Cleric can cast Sacred Flame (Cantrip) round after round until a three death saves have been missed. Other sources of radiant or magical damage should work as well, as long at the damage being done is magical, to speed up the process.
- I chose Sacred Flame as it does radiant damage, which prevents regeneration in vampires, but that may be unnecessary.

Examples:

• Paladin's Holy Smite
• Warlock's Eldritch Blast
• Rogue's magical dagger

Presuming that the Party keeps doing damage, and the Vampire misses enough death saves before it floats beyond their reach and through that crack in the wall that the party can't get through, am I right?

Is the Vampire Destroyed?

Damage at 0 Hit Points

If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death. (PHB, p. 197)

Question Restated

• Does inflicting further damage on the misty 0 HP state allow the party to destroy the vampire?

• Does the Vampire fail a death save as any other creature would, in the 0 HP misty state, when it takes any additional damage?

• Does the Vampire have an out that I don't see in the monster description or the rules?

A good answer will explain:

1. Whether or not the Vampire is destroyed via this method
2. If not, why not

Answer 1

Yes (probably)

Rules as Written, I think you can kill the 0-hit-point Misty Vampire by doing damage to it three times before it escapes to its resting place, or by doing massive damage to it (equal to or exceeding its maximum hit points).

But there is certainly room for disagreement, as the rules regarding creatures with 0 hit points are written in the context of creatures that are unconscious at 0 hit points, which the Misty form of the Vampire is not.

Honestly, I don't think the intent of the rules is to allow a Vampire to be destroyed in this way. It seems that the intent is that you have to follow it back to its resting place, drive a stake through its heart, and then destroy its body while it's paralyzed.

Rules around having Zero Hit Points

PHB p. 197 says

When you drop to 0 hit points, you either die outright or become unconscious....

Creatures that take massive damage die outright.

Otherwise they fall unconscious but are dying -- they must make death saves to determine if they eventually stabilize or die outright.

There are three exceptions wherein a creature may be stable at 0 hit points -- still unconscious, but not needing to make death throws.

1. If the attacker decided to strike an incapacitating blow rather than a fatal one to take the creature down to 0 hit points [PHB p. 198]
2. If the creature is stabilized by another creature (by making a medicine check [PHB p. 197], using a Healer's kit [PHB p. 151], or by using the Spare the Dying cantrip)
3. If the creature stabilizes by rolling three successful death saving throws before rolling three failed ones.

Note that in all cases here, a creature with 0 hit points is unconscious.

Normally there is no way for a creature to be at 0 hit points and still be conscious and taking actions. However, the Vampire is clearly an exception, based on the text of its Misty Escape feature. It is very unclear whether any of the usual rules that apply to unconscious creatures at 0 hit points also apply to Misty Vampires at 0 hit points.

So What Rules Apply to a Misty Vampire that is Stable and Conscious at Zero Hit Points?

The description of the Vampire clearly admits the possibility of doing damage to the Misty Form by magical means.

Taking Damage at 0 Hit Points (PHB p. 197):

If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage equals or exceeds your hit point maximum, you suffer instant death.

And:

On your third [death saving throw] failure you die.

Note that a creature that takes damage while at 0 hit points that isn't enough to kill it outright remains at 0 hit points. 5e does not have a concept of negative hit points.

Two Ways to Kill the Zero-HP Vampire (RAW):

1) damage it three times, causing it to fail three death saving throws before it has a chance to stabilize or be stabilized by any of the means listed above

2) damage it once, for an amount that equals or exceeds its maximum hit points (perhaps a massive Paladin critical smite)

Caveats

1. If the Vampire has not used up its Legendary Resistances for the day, it can choose to succeed on its first three death saving throws, so you would have to hit it additional times to get three failed death saves that "stick".
2. It is very unclear whether any of the usual rules that apply to unconscious creatures taking damage at 0 hit points are also meant to apply to conscious Vampires in Misty form at 0 hit points (but RAW I believe there is nothing to override them).
3. It is possible that the Vampire's Misty Escape kicks back in and stabilizes the Vampire every time it gets hit, removing method 1 as a possibility (but I don't think so, see below).
4. It is possible that Vampires are meant to be immune to failed death saving throws (but I don't think so, see below).

On Misty Escape Re-stabilizing the Vampire

Clearly when the Vampire first drops to 0 hit points, the Misty Escape feature permits it to be stable and conscious where ordinarily it would be neither of those things.

If the Misty Escape feature triggers each time the Vampire takes damage while at 0 hit points, it could be argued that the feature stabilizes the Vampire each time.

However, the trigger for Misty Escape is that the Vampire drops to 0 hit points (outside its resting place). Getting hit while already at 0 hit points and remaining at 0 hit points does not constitute dropping to 0 hit points.

On Immunity to Failed Death Saving Throws

PHB. p. 198 says that Monsters can sometimes make Death Saving Throws:

Monsters and Death:

Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.

Mighty villains and special nonplayer characters are common exceptions; the DM may have them fall unconscious and follow the same rules as player characters.

Note that this is given as an option for a DM to make a creature more powerful than a normal monster that just drops dead at 0 hit points. But we already know that a Vampire is not a normal monster that just drops dead at 0 hit points. Its Misty Escape feature is a stronger feature than the standard Death Saves feature that prevents PCs from just dropping dead at 0 hit points. So this clause in the PHB doesn't really apply in this case.

However, I don't see anything here to suggest, whether the DM usually gives monsters death saves or not, that any monster should be immune to dying after suffering three failed death saves at 0 hit points.

Answer 2

No

In D&D 5e specific beats general. The general rule is (PHB p. 197):

Dropping to 0 Hit Points

When you drop to 0 hit points, you either die outright or fall unconscious, as explained in the following sections.

and

Monsters and Death

Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.

Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.

The specific rule for vampires says (MM p.297):

Misty Escape. When it drops to 0 hit points outside its resting place, the vampire transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious, provided that it isn't in sun light or running water. If it can't transform, it is destroyed.

That specific rule short circuits the entire section in the PHB on reaching 0 hp and the DM can't (except via rule 0) have a vampire take the optional path. So vampires do none of those things; they roll no death saving throws so they can have no failed death saving throws.

Now, you can kill a vampire in this form but you must do it with massive damage; not failed death saving throws.

Answer 3

Questions in order:

Does inflicting a further on the misty 0 HP state allow the party to destroy the vampire?

Yes, but only if you exceed the instant death damage threshold.

Does the Vampire have an out that I don't see in the monster description or the rules?

Yes. Misty Escape isn't an unconscious or dead state, so there is no death save associated with the mist form being attacked. The specific wording for Misty Escape is found in the MM pg. 297 where it denotes that you do not fall unconscious. So a player hitting the form, even at 0 HP, doesn't incur a death save. You would need to exceed the massive damage threshold in order to destroy the form from an attack.

Now, in my opinion the specific wording of Misty Escape allows for creative methods to destroy or imprison the vampire. Emphasis in the wording below is mine.

Misty Escape. When it drops to 0 hit points outside its resting place, the vampire transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious, provided that it isn't in sun light or running water. If it can't transform, it is destroyed.

To me, this leads to a logical conclusion that a vampire in mist form can not enter sunlight or running water, else it would be forced to revert and be destroyed in the process. The water one is easy to conclude as gaseous forms treat liquids like solid surfaces and would be unable to pass through it anyways.

However sunlight is slightly harder; unless you simply consider that sunlight is a persistent single source of damage. This means the vampire would have 8 turns in sunlight (using it's average health and assuming that you're allowing it to travel through sunlight) before the mist form was destroyed because it took over 144 damage from a single source.