Any suggestions about players who constantly go to great lengths to capture enemies for the purpose of interrogation, even use healing potions or spells on them?

Another thing they do is frequently deal non-lethal damage to knock enemies out and get information from them. Although I've managed to handle each situation as it came along, it's starting to get a bit frustrating. I've considered making a house rule that makes it possible for non-lethal melee damage to still accidentally kill an enemy.

One specific scenario I have in mind for the next session is for them to encounter a high-level enemy NPC who is bleeding out. I would like for them to have roughly a minute or two to exchange some words (and get some clues), but then I want the NPC to die, and definitely don't want them to heal her. Is there any rule-based mechanic I could use for this (I have at least one player who is very well-versed in the rules, and can't just fudge things)? I thought of poison, but it wouldn't make sense in the situation (she is a wizard who was killed by another enemy wizard).

My opinion ( and solely my opinion ) here - with a possible alternate solution below the line break - is that isn't your call to make.

The Players are not actors; a D&D session isn't a screenplay you wrote. Let the players do what they will, and if your scenario can't adapt, then your scenario is poorly conceived and planned. Improvisation and adaptation are key skills for a DM. If you can't or won't do that, you're not DM'ing.

This is not a problem with your Players to be handled, this is difference between what you would like the outcomes to be and what the Players want as the outcome. 

Guess what? It's your scenario and planned adventure, but it's their game and their outcome. You don't get to determine the outcome of the unfolding events that finely. 

What you get to do is:

a) Set up the initial scenario.

b) Figure out the motivations and plans for all the other people in the scenario.

c) Figure out how you think the events would unfold and make plans for contingencies/scenes/encounters/conflicts that you can see possibly unfolding based on what would happen without the Characters, and what you think your Players are likely to do.

d) Adjudicate the Character actions, and the reactions of the NPCs and the world at large in a fair and ( largely, but not perfectly ) unbiased manner.

e) Discover what the story outcome is going to be, along with your Players.

If you consistently control the the scenario outcomes that finely, and why do you need the Players? You already know the outcomes. Heck, you're considering house-ruling combat - literally changing the rules - to get the outcomes you want. 

This is - I believe - a dangerous attitude to have which has the potential to eventually destroy your game. Let the Players catch on that you're controlling outcomes that finely, and they'll either stop trying, as they will - rightly - believe that their choices don't matter, or they start behaving randomly and chaotically trying to derail your pre-planned outcomes.

 That all said - if you really want to control the amount of information that the NPC is wiling to give the PCs right away because they'd then instantly solve whatever conflict you've set up as this scenario, then give the NPC motivation to not talk. She doesn't need to die.

Maybe something or someone she values will be put in danger if she talks. Maybe she's being blackmailed. Maybe she's under some sort of binding geas that prevents her from divulging the information.

All these conditions are problems which the Characters could potentially solve, to get the information: stop the blackmailer, break the curse, place the loved one under their protection, etc. This allows you to prevent the Characters from suddenly hitting the large ( poorly placed ) I-Win-Button ( if that is what it is ), but still gives them avenues to explore and adventure to unlock the rest of her information. It gives some nuance and details to your scenario, and doesn't force events.

But - Players doing things you don't want them to do isn't a problem with your Players, it's a problem between the kind of story you want, and the kind of story they want. That's a different order of problem entirely - but strong-arming events to trivialize your Player choices and forcing the outcomes you want isn't a viable solution.

I don't see a problem with players taking a non-lethal road to conflict resolution. If it makes them feel good, and they players are having fun, then SUCCESS!

I agree with the two above me. It can be annoying as DM to find ways to make player created situations work. However that is what we're there for. A totem barbarian in my group knocked a Kruthik hatchling unconscious and is trying to tame it as his pet. Didn't see that one coming, but it happens. Part of being a DM is to try and find a way to make such things work and let the players do their thing.

Remember that just because they capture an enemy and do interrogation it does not mean they will learn anything from it.  Perhaps the enemy does not know anything of value, or they dont roll high enough on intimidation. Perhaps the "monster" is a fanatic and rather wants to die than tell anything of value. 

In other words you dont always have to reward their approach but neither are you "punishing" their choice.

I always leave this option open for my players. Currently they are in a big city, so willy nilly killing people is a no-go. Even when assaulted, they should refrain from killing them. I've allowed them to simply make the call when they down the enemy if they kill or subdue. That said, I rule that not every weapon or ability is allowed to do so;

Damage from spells can't be non-lethal. A fireball to the face tends to hurt.

Damage from attacks that deal piercing damage can't be non-lethal. There's no way to use such weapons effectively without dealing tissue damage. Bludgeoning or slashing weapons often have a shape that would allow to use the "flat of the blade" or something similar thus these are allowed.

I really try to look in the moment if a non-lethal blow is justified and when it is not. If the barbarian rages and in a single blow crits and slams a guard with 9 hp for 21 points of damage, yeah he dead... I try to make it clear during the descriptions of most, if not all, their attacks just how effective their blows are. This helps in their understanding of how hurt the enemy is but also how effective that particular blow was; an enemy with 40 hit points is simply grazed by a spear throw that deals 8 points of damage, where aforementioned guard with 9 hp would get it in his lung or something. This makes the combat come alive and my players really seem to enjoy it. Do note; this works for my group, not for every one.

It can be really annoying if players keep interrogating the "grunts" of the campaign, mostly since you probably have not prepared anything. I try to wing it but it can be hard. I try to make it clear sometimes that talking is not an option. Some monsters like gnolls or skeletons simply put aren't very talkative. But it some cases it's fine if they talk to them. Often I just go "Ok, he wakes up and tries to get away, but after you calm him down he tells you that he's a hired goon that doesn't know much more other than that you were coming and he had to prevent you from passing". Remember that npc's have feelings too; if all npc's are fanatics that chug themselves at the nearest sword in order to provide xp to their wielder. This quickly becomes stale even if your combat is otherwise interesting. Have NPC's flee for their lives, regroup or live to harass them another day. This can allow for recurring villains or even an enemy turned ally if they spare his life.

I would not fight it and say that they can't keep enemies alive, again, unless you place a clear and understandable foundation. Just make sure your players understand and know these things beforehand and not spring it on them whenever. They might feel cheated upon and that can cause friction or even frustration.

Well everyone says too let the players heal and take prisoner as much as they want (and I agree), but here are some actual answers to your question:

The Band of loyalty from eberron.

You can make up a disease that prevents magical healing. You can work it into the story as a plague, even give it some saves and symptoms, and infect a player.

Make a spell that prevents healing like an extended form of chill touch.

Or use a continuous damage effect and healing will only prolong their suffering not save them.

I also fail to understand why this is a problem? 

Quote from DxJxC >>

Well everyone says too let the players heal and take prisoner as much as they want (and I agree), but here are some actual answers to your question:

The Band of loyalty from eberron.

You can make up a disease that prevents magical healing. You can work it into the story as a plague, even give it some saves and symptoms, and infect a player.

Make a spell that prevents healing like an extended form of chill touch.

Or use a continuous damage effect and healing will only prolong their suffering not save them.

While these are technically mechanical solutions, I'm not sure they're good dramatic solutions.

Is there some quirk of fate that only NPCs which the DM wants to die off have contracted this disease, or coincidentally been cursed by this particular spell? How about the Players - can any of them contract the disease ( or have an NPC use that spell against them ) and bleed out? How would the Players feel about that? Have you considered the campaign world impacts if this is a plague? Doesn't this suddenly render Clerical healing moot if most everyone has this - and if it isn't that widespread, then what are the odds that any given NPC has it? Doesn't that REALLY strain credibility that - coincidentally - all the NPCs that it would be convenient for the DM that they expire have contracted this?

Any Player smart enough to tie their shoes is going to figure out the DM is deciding ahead of time what the outcome is going to be, and you're back to Players ceasing to try or care about the scenario.

One specific scenario I have in mind for the next session is for them to encounter a high-level enemy NPC who is bleeding out. I would like for them to have roughly a minute or two to exchange some words (and get some clues), but then I want the NPC to die, and definitely don't want them to heal her. Is there any rule-based mechanic I could use for this (I have at least one player who is very well-versed in the rules, and can't just fudge things)? I thought of poison, but it wouldn't make sense in the situation (she is a wizard who was killed by another enemy wizard).

In this case, yes it sometimes is best to let an npc die since this can set some things in motion. If you want the players to be unable to heal using magic or skills, you could take a look at the bestow curse spell, since it is an enemy wizard that caused this. I would not put it past the possibilities of the spell, especially if it were cast at a higher level.

I think that particular case is a specific cited example - but in the OP it's clearly presented as a general problem.

There are other alternatives to straining believability, pre-deciding outcomes, and negating Player choices for no other reason than DM convenience. I sketched out a handful of ways of limiting NPC information, if that's the desired outcome.

Quote from Vedexent >>

I think that particular case is a specific cited example - but in the OP it's clearly presented this a general problem.

There are other alternatives to straining believability, pre-deciding outcomes, and negating Player choices for no other reason than DM convenience. I sketched out a handful of ways of limiting NPC information, if that's the desired outcome.

 True, but though it may be a general "problem" and it makes sense to help out with that, I just meant to say that OP was also enquiring about something particular, and I wanted to help out with that as well. This does not make my other post less legitimate in that I don't think you should disallow keeping enemies alive. Keeping enemies/allies dead is just as detrimental to most groups stories and games as keeping them alive would be.

Quote from Vedexent >>

I think that particular case is a specific cited example - but in the OP it's clearly presented as a general problem.

There are other alternatives to straining believability, pre-deciding outcomes, and negating Player choices for no other reason than DM convenience. I sketched out a handful of ways of limiting NPC information, if that's the desired outcome.

To be fair he did ask for solutions, in game, that a rules-lawyer couldn't argue. 

Give the detainee no information. No matter the torture the creature is put under they repeat that they know nothing. 

Make the victim a zealot that will die for the cause rather than divulge information.

Zone of truth doesn't mean they have to answer a question perfectly, just truthfully. Use that kind of mentality when giving answers during the interrogation.

Curses, Gaes, and Modify Memory are spells that could influence what the victim knows.

There's also a case to be made to homebrew a solution if it helps you present the story, example:

As the prisoner wakes, having taken 9 points of healing, you give him a chance to get his bearings. A solid punch landing in his face after he remembers where he is and what's happening. The body starts to convulse, twitching like crazy, the eyes turning black and a strange sludge drips from his ears. Your spells seem to have no effect, healing seems to have no effect. You watch as this strange insect like creature exits through the ear and immediately begins to burrow into the ground vanishing from sight.

Well, now there's even more questions, there's the implication of something more sinister, the information was never learned like you wanted. It's a good tool to use, however it's a very delicate tool, it should only be used in dramatic situations. This is not something that you would do to simply tell your players "You learn nothing from him".

So, agree with many that this is not really behaviour worth stamping out, but here are some suggesting to help you adapt.

1. The party likes to leave enemies alive? Let them pay a price for that. A goblin they captured escapes and dashes off to alert others. A kobold grovels for its life promising to serve the party, but all the intel it gives is lies and it steals something and disappears three days later. Good players might not like to kill everything, but enemies remain dangerous even after defeat.

2. Interrogation of enemies is often useless. Even torture is likely to produce false info. Let Insight be rolled against deception, and absolutely give the party false information presented as absolute truth.

3. For your NPC death scene, rather than have her dying of injuries, maybe have her trapped in some elaborate death machine (like the giant hourglass in Disney's Aladdin). Maybe there is some massively complex way to rescue her before she dies, but when the party start trying she can tell at them that something is more important, "Leave me! I've already tried everything. You must get the McGuffin to the alter before the ritual is complete! There's no time!" and so on and so forth. If they persist and do rescue her she is absolutely furious at them for messing up and thus further drama.

They seem intent on doing good deeds? Then let no good deed go unpunished. Let the players enjoy their characters wrestling with the tough choices.

BEGINNER DM HERE but i got a couple ideas that may have been said already but...

1. have the more intellectual or devoted npcs have a suicide pill embedded in their teeth so if they bite down hard in that area it breaks the pill and they die.

2. Some sort of bound magic spell on them that will set them afire or kill them outright if they try to reveal information.

3. if they are interrogating over long periods of time, add in a rescue attempt. 

4. have the creature spill its lifelong story to them instead, do this often enough they may stop trying interrogation 

as to your npc death if it is from wizard vs wizard

1. the NPC has used all its spell slots and is currently affected by some magic that is draining away its hp turn by turn and is nearly dead (figure out ways to delay them until it is dead)

2. The enemy wizard is in the midst of casting a spell that will kill the NPC

3. The enemy wizard has laid a trap that casts a spell (fireball maybe?) when the door into the area is opened, or when they try to rush in and save her, then you get to describe the scene of the NPC screaming in pain and suffering as they burn alive to the players and, if it was an npc they had promised to keep alive, how they have failed it, they let it die knowing its saviors were the reason it died because they didnt check for traps. IF you really wanna screw with your party or have them have a chance at vengeance maybe have the wizard enter after the trap ends to see what triggered it, as if he just popped out of the room to use the toilet or something. 

1- better to have care bears than murder hobbos.

2a - Have somebody assassinate the enemy wizard. why? Nobody needs to know yet -- just smile at the players.

2b - When she goes to 0 hp, her body begins to rot, her skin peals away from putrid corruption, the body rises as a...

2c - When the wizard goes down, the party begins to question her, shortly thereafter, her body convulses, and her head splits open to reveal...

Quote from Vedexent >> 

While these are technically mechanical solutions, I'm not sure they're good dramatic solutions.

Is there some quirk of fate that only NPCs which the DM wants to die off have contracted this disease, or coincidentally been cursed by this particular spell? How about the Players - can any of them contract the disease ( or have an NPC use that spell against them ) and bleed out? How would the Players feel about that? Have you considered the campaign world impacts if this is a plague? Doesn't this suddenly render Clerical healing moot if most everyone has this - and if it isn't that widespread, then what are the odds that any given NPC has it? Doesn't that REALLY strain credibility that - coincidentally - all the NPCs that it would be convenient for the DM that they expire have contracted this?

Any Player smart enough to tie their shoes is going to figure out the DM is deciding ahead of time what the outcome is going to be, and you're back to Players ceasing to try or care about the scenario.

 Drama is what you make of it. Mechanical solutions is what he was asking for because he has a rules lawyer player.

The spell was for the specific scene he had planned. If the players get infected by the disease, I did say to give it saves, and it only prevents magical healing, death saves and recovery from rest are still a thing, and I didnt say anything about not being able to magically cure the disease. If they confront the wizard who has the healing preventing spell, if it has a save and concentration, I see no reason it couldn't be used on them, its a good threat.

And if all these ideas are used properly, I don't see why players would complain. Maybe only a specific group has given all its low rank members a band of loyalty and the PCs can notice the ring and know they need to capture him without dropping him to 0. A NPC with the disease might show symptoms the party can recognize, and can still be knocked out with non lethal hits.

I agree with most of the above. Roll with it rather than resisting it. RP opportunities are awesome.

Having said that, I do have a rule requiring a skill check against DC 20 (hard) to knock out rather than kill during combat (or more precisely, to select the outcome), and allow the characters to trade -1H for each +1 on the skill check, decided before either roll.

Thanks for all the input everyone.

To address a common theme, I would like to point out that I can easily "deal with it" and just roleplay the interrogation. And I have done that. My question is not about what to do when the party unexpectedly gets to interrogate an enemy. My question is about when the party does that same thing over and over again. I don't want to roleplay twenty interrogations of goblins and kobolds. 

Anyway, thanks for all the suggestions, I think I have a good idea of how I'm going to handle that dramatic scene!

Quote from RegentCorreon >>

So, agree with many that this is not really behaviour worth stamping out, but here are some suggesting to help you adapt.

1. The party likes to leave enemies alive? Let them pay a price for that. A goblin they captured escapes and dashes off to alert others. A kobold grovels for its life promising to serve the party, but all the intel it gives is lies and it steals something and disappears three days later. Good players might not like to kill everything, but enemies remain dangerous even after defeat.

 

This one right here. If you play out reactions realistically, and go around sparing enemies consistently, then it's likely one of them will turn around and back-stab you.

“If you pick up a starving dog and make him prosperous he will not bite you. This is the principal difference between a dog and man.”

― Mark Twain