What happens when an unconscious but stabilised character is hit?

Question

At the end of this answer to a different question ("If you succeed on all of your death saving throws, what happens?"), the answer states that:

If an unconscious character is attacked, the attacker will have advantage on the attack (if melee) from the Prone condition; if it hits, it will be an automatic critical hit because of the unconscious condition which is 2 death save failures.

I just wanted to clarify exactly what happens in this scenario; let's say the scenario in this case is a creature is attacking a downed but stable PC. In both cases below, assume that the PC just made their third successful death saving throw and is now stable but still unconscious, and it's now the monster's turn.

Is it:

1. • PC is unconscious and monster attacks and hits;
   • PC takes damage and is now back to making death saving throws;
   • since the PC just took damage (and a critical hit, no less, as per Unconscious condition rules), they immediately suffer two death saving throw failures;
   • on this PC's next turn (assuming there is no intervention by allies), when they roll a death saving throw, they may die if they roll below 10.

Or:

2. • PC is unconscious and monster attacks and hits;
   • PC takes damage and is now back to making death saving throws;
   • the damage taken is what put them back on death saving throws, so they do not immediately take two failed saves;
   • on this PC's next turn (assuming there is no intervention by allies), when they roll a death saving throw, they are currently on no fails and no successes, so they have no chance of dying this turn.

Answer 1

The creature takes death saving throw failures on the initial hit

Unfortunately for the character in question, your first scenario is correct.

A stable creature is unconscious with 0 hp - the fact that they are currently exempt from having to make death saving throws (and that the number of successes/failures they have previously made has been reset) is irrelevant.

The rules for death saving throws state:

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.

So, as a stable creature has 0 hp, any damage it suffers causes at least one immediate failed death save.

Damage should still be rolled to check for Massive Damage, and if the attacker is only 5 feet away from the character, it is an automatic critical, meaning two failed death saves.

Then, further compounding the character's misery, on its next turn, it must also resume making death saving throws.

The creature stops being stable, and must start making death saving throws again, if it takes any damage.

Answer 2

I think option 1 would be most likely.

Taking damage while unconscious, whether stable or not, would be a Very Bad Thing.

In the Damage at 0 Hit Points section it states:

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

This particular section makes no mention of whether the creature is stable or not - only that this rule comes into play if they are at 0 hit points.

While, a bit further down under the "Stabilizing a Creature" section it states:

The creature stops being stable, and must start making death saving throws again, if it takes any damage

Since these two scenarios are not exclusive, they presumably both occur when an unconscious but stable creature takes damage: They suffer automatic death saving throw failures from the hit and then also start making death saving throws again.

I can see there is room for ambiguity, so a DM may opt to be lenient, but I would still lean towards your 1st interpretation as being more RAW.

Answer 3

The PHB states

The creature stops being stable, and must start making death saving throws again, if it takes any damage.

From this i think both are valid interpretations of the presented text.

Answer 4

The creature stops being "Stable" and makes Death Saving Throws normally

A stable creature doesn't make death saving throws, even though it has 0 hit points, but it does remain unconscious. The creature stops being stable, and must start making death saving throws again, if it takes any damage. ...[snip]

Stabilizing a creature removes it from the death saving throws "section" of the rules, so it would be your second interpretation:

2. • PC is unconscious and monster attacks and hits;
   • PC takes damage and is now back to making death saving throws;
   • the damage taken is what put them back on death saving throws, so they do not immediately take two failed saves;
   • on this PC's next turn (assuming there is no intervention by allies), when they roll a death saving throw, they are currently on no fails and no successes, so they have no chance of dying this turn.