Allowing instant kill (skipping a resolve) in a very specific situation

Question

I faced an argument while running DnD 5e as a DM.

A player (rogue) had devised a very meticulous and well thought-of plan to assassinate an NPC - A veteran soldier with 64 hitpoints. Still just a normal human character with no magical gear or capabilities except of those used in combat.

The player also managed exceptionally well in a few perception and stealth checks leading to a situation where he managed to be next to the sleeping enemy, without being noticed at any point, ready to assassinate the target.

As a DM I sometimes skip certain resolves, if the situation the player is in, is thanks to already successful resolves and exceptional role-playing and planning from the player's part. Adding to the story and experience of all. I encourage that.

So in this situation I thought that it is likely that even with advantage and critical hit, the target would not get killed by the player's first strike, initiating a combat situation where all the great effort, planning, previous resolving, narration and culmination of a juicy assassination mission would've gone down the drain possibly just because the target character had some HP left in a situation where he's deep asleep, in normal clothing with the assassin having all the time in the world and the blade on his throat.

So, that likelihood in mind, I felt this is one of those rare situations where resolving would "get in the way" of good, well-deserved conclusion to a series of actions and decided that all things considered, in this rare situation and as a reward of great role-playing, planning and previous difficult resolve checks, he manages to just end the life of his target without resolving hit and damage.

One player insisted that it was the wrong thing to do, that we should resolve the HP.

Am I as a DM allowed to allow instant kill like this? Is this appropriate, considering all those things mentioned?

Answer 1

It's perfectly fine. You, the DM, made a well-thought out exception to the rules in the interest of a good story. That's not just OK, that's your job.

Now the question is, why did that other player object? Are they just trying to follow the rules strictly, or for some other reason? Either way, you should talk to them and find out. Then the two of you can agree on when and why such exceptions are okay.

Answer 2

For the greater good of role play is a fine way to DM, except...

you need to establish that ahead of time.

Look at the Dungeon Master's Guide about dice rolls

There is a chapter in the DMG about running the game, but it's after the chapter on magic items so most people never get that far.

In particular, there is a section called "The Role of Dice". I'll quote a few pieces:

Dice are neutral arbiters. They can determine the outcome of an action without assigning any motivation to the DM and without playing favorites. The extent to which you use them is entirely up to you.
...
Some DMs rely on die rolls for almost everything. When a character attempts a task, the DM calls for a check and picks a DC. As a DM using this style, you can’t rely on the characters succeeding or failing on any one check to move the action in a specific direction. You must be ready to improvise and react to a changing situation.
Relying on dice also gives the players the sense that anything is possible...A drawback of this approach is that roleplaying can diminish if players feel that their die rolls, rather than their decisions and characterizations, always determine success.
...
One approach is to use dice as rarely as possible. Some DMs use them only during combat, and determine success or failure as they like in other situations...With this approach, the DM decides whether an action or a plan succeeds or fails based on how well the players make their case, how thorough or creative they are, or other factors.
A downside is that no DM is completely neutral. A DM might come to favor certain players or approaches, or even work against good ideas if they send the game in a direction he or she doesn’t like. This approach can also slow the game if the DM focuses on one “correct” action that the characters must describe to overcome an obstacle.
...
Many DMs find that using a combination of the two approaches works best. By balancing the use of dice against deciding on success, you can encourage your players to strike a balance between relying on their bonuses and abilities and paying attention to the game and immersing themselves in its world. Remember that dice don’t run your game — you do.

Heavy stuff...but it shows that there different styles of how to handle dice as part of the game. In High School, I would play with a couple people as we walked between classes. No dice what so ever, just describe your action and the DM would let us know if it worked or not. It was combat light, with more puzzle and exploration, but it was fun.

But if the DM ever said, "Okay, roll a d20 to see how well you did," we would literally have to stop in our tracks. Who has a d20 handy with an arm full of books? This sudden change of mechanics would make us wonder what else would be sprung on us. Sort of like the pop quiz we were about to walk into...

Back to Session Zero

You mention, "As a DM I sometimes skip certain resolves..." That would normally be an indicator that you've already set a precedence that you don't rely solely on dice rolls. But it sounds like, at least to the player that is complaining, that you haven't made this well-known to your players, or that you didn't foreshadow this situation well enough.

Players need to be aware not just of the rules, but how you implement the rules so no one is caught off guard. Just like in High School, we knew that dice were not going to be used. But maybe the DM could have added a caveat about combat; "For combat, we need to use dice, so if there is an encounter, we need to wait until lunch so we have a table to roll on."

You need to make clear the rules of engagement; "There are going to be times where I'm not going to let the dice decide. Like if the there is a situation that you can't fail, or if you role play/describe exactly the action needed to succeed. There may also be time where you'll need to succeed on a lot of checks to create a winning situation so that the end is worth all the trials."

Now with that ground work, you can play on.

Then during the game, give hints that what they are doing now will make things easier later; "Since you did x, I'll say that y happens." This could be disabling the alarm system means that if the party encounters guards, they can't easily call for back up. Or that they cast a silence spell in a clever way, no one will accidentally walk into it and get suspicious.

This also goes for dice rolls. "Since you rolled so high..." as the hip DM's say.

There is always one in the crowd

In the comments on Jorn's answer, you call out the one player:

• "picking the best possible multi-class combination and min-maxing everything"
• "maybe he doesn't like an enemy getting killed without resolving, because in such situation his rule-exploiting damage chains don't get to shine"
• "I'm not judging a play-style"

One, I think you are judging, but that's besides the point. Two, you're not going to please everyone. But you can at least min/max the damage (see what I did there) by making sure everyone is on the same page as far as how you do your game. If their character only "works" because of dice rolls, and that's how they want to play, then letting them know ahead of time that there are situations where you don't care about dice, you care about role play, then that player can make choices.

I have characters that work very well due to how classes/feats/spells/features/items work in synergy. But that character also has a complete back story explaining WHY they have that combination, so even if I don't get to roll 20d6 damage because the rogue got in a coup de grace, I still have a character I can speak through.

Answer 3

This is "often appropriate"

The DMG Section on Using Ability Scores (p.237) says:

When a player wants to do something, it's often appropriate to let the attempt succeed without a roll or a reference to the character's ability scores. For example, a character doesn't normally need to make a Dexterity check to walk across an empty room or a Charisma check to order a mug of ale.

In your world, do the characters have to make Charisma (Persuasion) rolls every time they order a mug of ale? If not, then you are already choosing to make success automatic in some cases. In this particular case, because of all the "great effort, planning, [and] previous resolving" of the player, you have determined that the assassination would be an automatic success. Not only do the rules permit you to do that, but they encourage you to.

To be fair to the objecting player, this section of the DMG continues:

Only call for a roll if there is a meaningful consequence for failure. When deciding whether to use a roll, ask yourself two questions: Is a task so easy and so free of conflict and stress that there should be no chance of failure?
Is a task so inappropriate or impossible- such as hitting the moon with an arrow-that it can't work?
If the answer to both of these questions is no, some kind of roll is appropriate.

The objecting player might say that there is a meaningful chance of failure - but that is confusing a chance of failure with a consequence of failure. Setting aside the the 1-in-8000 chance¹ that the rogue would 'miss' the first round, even if they hit and do many dice worth of damage², it is possible that the NPC might survive after the first blow if the rogue rolls very poorly on all those dice. So yes, they might not kill the NPC after one hit, but what happens then? If there are guards near enough that they can be alerted with one cry, then your rogue hasn't really done all the preparation necessary for automatic success. But if what this really means is that you will play out two or three rounds of combat in which the rogue fights an unarmed and unarmored opponent who has only a few hp left, then there isn't actually a meaningful consequence of failure. It is just prolonging a forgone conclusion.

Is this combat?

One might be skeptical that an assassination attempt can be compared with walking across a floor. Can a DM actually permit a PC to kill an NPC without combat? Well, what is combat, according to the PHB?

The clatter of a sword striking against a shield. The terrible rending sound as monstrous claws tear through armor. A brilliant flash of light as a ball of flame blossoms from a wizard’s spell. The sharp tang of blood in the air, cutting through the stench of vile monsters. Roars of fury, shouts of triumph, cries of pain. Combat in D&D can be chaotic, deadly, and thrilling.

Does this sound anything like the assassination attempt? D&D is not a simulationist game - it does not attempt to realistically portray the damage a blade might do to the body of an opponent, nor the chance of being able to place it correctly. Rather, it attempts to capture the drama, struggle, sturm und drang of violent conflict. Presumably your rogue has had this experience already - securing floor plans of the NPC's lair without knowing whether they were accurate, sneaking in and overcoming the guards through stealth checks and perhaps even combat. What remains is not tension and excitement, but dramatic reward for their efforts. If there is any chance the NPC will live, that they will be able to call out and bring aid, that they will be able to reach their potion of gaseous form and escape, then you should roll out the combat as normal. But if you have extracted the last drop of drama from the situation, it is no longer a combat; it is just tedious dice rolling. If the NPC survives the first blow, but is severely wounded and cannot realistically harm the rogue before they are cut down, spending those few rounds of rolling does not create the excitement that combat is supposed to engender. Rather it removes the drama and replaces it with frustration.

In the game I DM, the party is currently in the underdark. They came upon, and had to pass through, a partially collapsed tunnel whose near end was infested by shriekers. The shriekers themselves posed no combat challenge to the high-level party, but the possibility that they might shriek and warn or attract other monsters did. The ranger approached carefully - was his Perception good enough to see them all? Was his Stealth good enough to get a spell off (silence) before they could note him? Was his Arcana good enough to place the spell to include them all in the area of effect? That was the drama of the situation. Once those had all been accomplished, the mage remained at a distance and roasted them all with firebolt. Now I could have forced the mage to roll to hit, because a miss was possible. And I could have insisted that she roll damage, because even with 3d10 a low roll might result in a shrieker surviving. But at this point, we were no longer in combat. Absent dramatic tension, it was just dice rolling. The only consequence to not one-shotting a shrieker was that the encounter would take six seconds longer of game time so that she could roll again. Once the ranger had achieved his goals, I just narrated the mage roasting the shriekers without a roll being made.

Consider what the DMG (p. 82) says about Combat Encounter Difficulty:

There are four categories of encounter difficulty.
Easy. An easy encounter doesn't tax the characters' resources or put them in serious peril. They might lose a few hit points, but victory is pretty much guaranteed.

What about situations even less challenging than easy? If your rogue, like my mage, faced a situation that did not use their resources at all, put them in any peril, and in which victory was guaranteed, that is not a combat encounter. Getting to that point was likely several combats, but once the rogue's knife was against their helpless opponent's throat, it is no longer combat. One might think that "Attacking a creature is pretty much a call for an attack roll by the book," but remember what the PHB says:

If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making an attack roll, you're making an attack.

Here, the inverse applies - if the DM doesn't call for an attack roll, you aren't making an attack.

What are hp?

Hit points?

Hit points represent a combination of physical and mental durability, the will to live, and luck.

During the rough-and-tumble of combat, the NPC's trained combat reflexes make most blows that land wounds, and they survive those wounds through a combination of durability, will to live, and luck. But sleeping is simply a different story. It is perfectly appropriate for you to rule that no amount of will to live helps you when a trained assassin has slit your carotid artery with a sharp knife, and no amount of luck is of aid when they later plunge that knife through your eye and into your brain stem. In this case hp are not relevant; you simply die. If an NPC was on the executioner's block, I would not worry about how much damage an axe does; no amount of hp keeps you alive after decapitation. Despite the objecting player's min-maxing optimization of damage in combat, this is not a combat situation, and the the concept of hp don't apply.

As SeriousBri states so well, theirs is not a rules objection so much as an existential crisis in realizing that they are not prepared for all aspects of the game. I join NautArch's call for SeriousBri to submit their insights as an answer so that we can all upvote it.

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¹ _{With proficiency bonus and dexterity mod against an unarmored opponent, they are probably going to miss only on a natural 1. They have multiple sources of advantage (unseen attacker, unconscious opponent, possibly assassin subclass with a surprised opponent), so only a 1 in 400 chance of rolling 2 x 1N. In that unlikely event they can use a free object interaction to draw a second blade and attack with a bonus action a la two-weapon fighting for a third chance to hit, so only 1 in 8000 chance of rolling 3 x 1N.}

² _{So long as they hit with a source of advantage (unseen attacker, unconscious opponent, possibly assassin subclass with a surprised opponent) they can use their rogue Sneak Attack, and this dice pool will be doubled since all of the rolls are automatic criticals (attack on unconscious opponent, possibly assassin subclass with a surprised opponent).}

Answer 4

Most of these responses have focused on the role of the DM in determining the expectations with the players around scenarios like this. But I do want to point out that there is a rule to help support your ruling in this situation.

In the DMG pg 273, there is an optional combat rule for Massive Damage which says that when half or more of a creature's HP is done from a single source of damage, the creature can roll a Con save (DC 15) and if failed potentially reduce the creature to 0 HP (among other randomly determined effects). Of course, if you are using this rule you would need to use it in all appropriate situations, PCs included, which again goes back to making sure outcomes like this are clear and up front with players.

But at least in this case, you have a rule to point to as to why a situation resolved the way it did.