What would an organization of bounty hunters need to neutralize any player character?

Question

I've never had an issue with murder hoboes in my own campaigns, but I want to be prepared in case players think they can bully figures of authority or cast powerful spells that would be considered basically terrorism. I'm also just curious to see if there's a way to boil down what a normal society would do to protect themselves specifically from the powers of 5e D&D player characters.

Suppose there's an organization of bounty hunters that are specifically trained with the tools, knowledge of every class, race, and spell; and skills to neutralize criminal adventurers. What tools and skills would they have? Here are some I can think of, but I'm curious what bases you guys can help me cover:

• Dimensional shackles to prevent teleportation escape
• Spellguard shields
• Mage Slayer feat
• Instructions to behead (or perhaps disintegrate) adventurers that they have to kill, to prevent resurrection and speaking with the dead from their allies
• Spells like hold person, see invisibility, mind blank, silence, silvery barbs, heat metal, counterspell, and dispel magic
• Maybe fire shield to punish players with a lot of Extra Attacks?
• Possibly high level spells like forcecage, antimagic field, invulnerability, foresight, and time stop

What else would they have in their toolkit? Are there capabilities I'm forgetting about?

Answer 1

Numbers!

It doesn't take skill or ability or even legendary actions if the bounty hunters or guards can flood the player characters and stomp them with sheer numbers: if an army of a hundred pack-tactic Kobolds with light crossbows, deployable cover walls, and alchemist fire flasks arrive and turn whatever is in the area of the PCs into a pincushion, then even if the PCs could kill a dozen in a round, the sheer amount of attacks means guaranteed hits. If about 20 of Tucker's Kobolds were bad (and arguably are more lethal now), an army of them would manage to whittle down the PCs within a couple of rounds. If those Kobolds even get a few class levels, then it is arguably even worse for the PCs, even without a single spell or bonus feats: Dungeons and Dragons has, since the first editions, one fact that holds true: The number of attacks often determines the outcome more than the quality of attacks.

Polymorph!

Polymorph isn't seen as a typical combat spell to attack with most of the time, but it is surprisingly effective: the PCs with the worst wisdom save tend to be those that are physically the most dangerous. Turning those into creatures that are considerably lacking in combat capabilities - like a sheep - and then not damaging but grappling them can reduce the party's capabilities quickly.

Divide et Impera!

Divide and Conquer - the classic saying, accredited to Philip II of Macedonia, holds true in many situations. If you can make sure to pick the PCs split up and alone - such as attacking them when they split up to do things in town or while they sleep in different rooms - numbers advantages can be gained even from a much smaller group: outnumbering the 5-party gang 5:1 takes 25 goons, but getting them one by one only takes 5 people. If you calculate how much damage you need to dish out in a single surprise turn to KO each PC, then pick them one on one so they are taken out...

Caveat Emptor!

A dedicated group of PC-killer NPCs might sound fun for you as a GM, but it is at best FUN^TM. The Dwarf Fortress kind of fun. You know, the Losing is Fun! type. Being on the receiving end of any such tactics that are dedicated to first cripple PCs group advantages and then killing them is about as fun as the classic "Rocks fall, everybody dies". Or to phrase it clearly: It's only fun for the DM, while it is typically very frustrating and unfun to be on the receiving end. Unless your players are dedicated masochists and love to see their characters suffer and being hit hard, don't do this.

But if your players are in this for the drama and suffering... well... then, with the consent of everybody around, you all shall have your FUN^TM

Is there a good TPK?

I have learned from many GMs that a TPK is usually an accident. And if they planned it, they tried to make it epic. Not an ambush in the night, or a gargantuan monster just stepping on the party, or the tunnel caving in. No. The death of the PCs must mean more than just the end of this chapter in the campaign.

In one case I witnessed, it was a fight to the death against a literal army of monsters and the players knew that for each round they could hold with a single PC standing, a group of people would manage to escape the sieged town. When the last player fell, the GM gave them a narrative of how many lives their sacrifice saved - and everybody went home with some accomplishment, even if it sucked to have lost their characters. It was a tale to tell.

In another event I was part of, the players' final stand was only run cinematically. Each player described how they found their death on the battlefield of their side against an enemy, mowing through units like a legendary hero - only to succumb to wounds in the end. The players knew from the start of the session "Today is where your character dies." They even knew from the end of the session before. I remember how one player had prepared a pre-battle speech and another wrote a last diary entry for their character. The players had taken their time in preparing to give their characters a farewell, and it was epic. No dice were rolled that evening, just glorious, freeform storytelling.

Answer 2

A Case of Mechanics vs. Ability

Not to deep in this stack exchange you'll come across this question. In it is described a scenario of very easily slain minions and how you might utilize them to their fullest potential. Then it simply becomes a matter of scale. Your bounty hunters can be as scary as you want them to be, given the proper preparation. And assuming you're utilizing more homebrew than not, nigh on impossible to defeat.

My particular answer will be based on a simple premise. You need very, very little mechanical might to make a truly terrifying encounter.

Time & Preparation

In my own campaign, I unleashed the final enemies on my players with 2 simple pieces of knowledge. They'd have time, and they'd be prepared. So when the fight started, they had the element of surprise and that's all they needed. Before round 3 they had accomplished their goal (besides scaring my players) and looked to make a casual retreat. So to you I recommend the same. Give your bounty hunters the benefit of time and preparation. That way they go into "the hunt" with character knowledge (not player knowledge).

If your bounty hunters have time and knowledge they can set the stage much more effectively and utilize spells that last so that they don't need to take up slots during the fight. Dimensional Shackles are nice if you need to transport a creature that still can cast spells. But a Private Sanctum will make sure that they don't get that opportunity during combat much easier. A Forcecage may be extremely hard to deal with but a Wall of Force can trap people inside a private sanctum where they are caged just as well while allowing a well placed Sickening Radiance to make short work of a fight.

Even lacking spells, a few traps can separate a party and make the subsequent hostage situation very tenable. A couple of tension snares, a punji pit (or just a pit), or even bear traps will change the dynamic of a fight immediately and harshly.

Spellcraft in practice

You list a bunch of high level spells and the oft used Silvery Barbs/Counterspell. Simply put, those spells are useless if you get the jump on your quarry. A single surprise round will put many a player on the back foot and even more so when they come up against a group as organized (or often more organized) as their own. In my own example above you also would never be in range for those spells (and they wouldn't be in range against you either).

Likewise you have a lot of spells that act as "reactive" spells. See invisibility, Dispel Magic, Heat Metal, all of these are either only as good as the players make them or take too long to give a desired effect. Assuming you're attempting any form of balancing this leaves very few slots in a lot of key areas like 3rd or 2nd level where more hard control or damage spells can be.

Summarizing the importance of tactics

I understand that there's an urge to add mechanical might to creatures when we want them to be scary. I'm guilty of doing just that. But mechanical might only goes so far and the biggest capability lost when designing creatures this way is their mind. If forced, these bounty hunters will be hunting your players. So they will be baiting traps, setting ambushes, and utilizing spells that can't be flicked away so easily by any party composition. They'll perform information gathering operations, separate the party as efficiently as possible, and only take fights they think they can win. Then let the dice roll and see where they land knowing they've rigged them in their favor.

Answer 3

Use incentives, not punishment

There are more effective ways to keep players being murderous cretins than retribution and punishment. In my experience, players generally don't enjoy losing or being beat up, while they do enjoy being appreciated.

Give them social relationships that matter. Reward good behaviour, with gold, services, gratitude of the populace, friends, and successful outcomes of plans. Have not every ally or encounter betray them eventually, so they don't learn to better kill first. And so on. Giving them a reason to not be murder hobos, by showing them it leads to good outcomes is more effective and more fun than putting them down with superior force.

Retribution measures

But, you ask about retribution, so let us address this. It would not make sense to list specific features, because powerful NPCs can be built like PCs, and can have access to literally anything a PC could have access to, wether these are magic items, class features, or spells. DMG p. 92:

When you give an NPC game statistics, you have three main options: giving the NPC only the few statistics it needs, give the NPC a monster stat block, or give the NPC a class and levels.

In addition, they can be allied with creatures and monsters of any CR, from the monster manual and otherwise. And, as you tagged your qeustion homebrew, NPCs are of course not limited to what is available to player characters, they can have other powers, tools, and features that you as the DM deem appropriate.

Depending on the world, the most powerful NPCs are of much higher level than the PCs for most of the PCs career. Most play happens in tier one and two, while powerful NPC spellcasters that have been published, or even NPCs from the monster manual have access to spells up to 9th level, meaning they have spellcasting abilities comparable to a 17th level character.

In very practical terms, if your PCs want make it all the way up to level 17, they need to learn not to piss off those powerful NPCs along the way.

Magical medieval society

When it comes to society, nobody is an island. Even the little hamlet that has no means to defend themselves from a level 7 party that wants to throw their weight around is part of someones fiefdom, and that someone will not be amused. If the PCs cause trouble enough, and for long enough, what they do will eventually trickle up to someone who is powerful enough to put a stop to it.

The basic idea hear is that society protects itself by escalation. If they cannot deal with the PCs with local forces, like a group of city guards, the escalate to more powerful defenses, and in a magical fantasy world, such powerful defenders exist.

Imprisonment. You seem to assume one answer to such misbehaving PCs is imprisonment by bounty hunters, and from looking at your list of measures, seem concerned on how to contain spellcasters. There is a whole question on that. The simplest, mundane way is to gag and tightly bind them, so they cannot use verbal or somatic componetns, and strip them of all foci and material components.

Execution. You also can have stricter laws, that punish murder with being put to death yourself. Dead PCs don't cast spells. I however would be careful -- it is easy to do that, but the question is, do you want to do that?

Answer 4

First, be careful: Work for it enough, and you can get close enough to "Rocks fall, everyone dies" as to make no difference. Tread lightly. You might have better luck simply talking to your players directly about why murderhoboes just mean the game isn't working for you. If you're sure you want to go this route... Quit screwing around and go for the throat.

Players have myriad ways to break the game. You have access to exactly the same stuff. A large enough society will have others of similar power levels to the PCs, and bad enough murderhoboing can and should draw their attention, if they're using WMD (like unleashing undead-creating creatures like a Blight Lord in a major population center). Let's call them the Anti Murderhobo Force (AMF).

Legendary action

You tagged this with homebrew. Give the AMF legendary actions. Homebrew a broken Legendary Action: (3 actions) I am the law Reaction: A target of a spell you cast succeeds on a saving throw. Effect: The target must save again with Disadvantage.

High level spells

Of the high level spells, time stop is good. But you can do better. Use the Legendary Action in conjunction with True polymorph or Feeblemind or Imprisonment. To say nothing of a group of casters that all know Wish. Why beat around the bush?

Divination

Everyone knows to never underestimate scrying. And yet, they do it anyway, all the time. Listen to your players' murderhobo plans, then screw them over with the fact you know what they're going to do and exactly how they plan to do it. Point to high-level scrying and say "they cared enough to scry your every move". Or tell them a multiclass Druid/Bard/Rogue Wild Shaped into their camp then employed the Charm/Modify Memory combo mentioned here.

Read that other page

If you want to go by the book, you can replicate a lot of what that link says with appropriately-built PC class combos.