D&D 5E What are your tips for making mobs/swarms interesting?

[MNblockhead]

With swarms larger than M, I give them one attack against every target inside the swarm.

I once had a huge swarm of snakes that I gave an opportunity attack against anyone who moved whilst within the swarm. That proved pretty lethal as it occupied most of the room.

I also created this:

I love the Swarm of Iridescent Butterflies! Thanks for sharing!

 

[NotAYakk]

Legendary actions makes them act on more initiative counts.

Saves bypass armor. Even goblins can force a str save or be knocked prone and restrained by a swarm of goblins.

I like the idea of HP based on morale. But it should then get saves to maintain morale, like zombies but not con. Or like barbarians.

 

[Quickleaf]

I'm running a mega dungeons where not infrequently, the parties will run into a large number of baddies. E.g. giant rats, fire crabs, and even goblins. Also, swarms of rats, bats, and insects.

As I DM I've been finding the mobs a slog to run and the swarms boring.

I could treat a large number of rats, for example, as a swarm, with jacked up stats, but then you loose the chaos and uncertainty of having attacks happen throughout the initiative order. I've also tried to using the mob-combat rules in the DMG. The mob rules are good because they give a certain number of hits per turn, saving on lots of roles and ensuring that a mob is a threat even to characters with high ACs. But having all the creatures act on the same turn changes player strategy in a way that makes the combat more boring.

Similarly, I hat how swarms generally have a single attack, making them a danger to a single player at a time. The solution to that is multiple swarms, so, fine. But then many swarm attacks have trouble hitting high armor classes, which is not a reasonable result. Why would a swarm of tiny insects be hindered by platemail? If anything, having a lot of armor would be worse as you can easily shake out the creatures or swat at the creatures that got below your armor.

For mobs, I've gone to using tools to handle large numbers of combatants so they can attack throughout the initiative order. I've used Hero Lab, but now use Improved Initiative. But but I miss the auto hit rules of mob combat. I'm thinking that when there are a large number of combatants, I can have members choose to attack on a lower initiative order until there are enough attackers for an auto hit and they will continue to act together on the same round. That gives the sense of a character truly being ganged up on. So, their may be the chaos rush of, say, goblins, but they will start to cluster together around individual PCs.

For swarms, I've thought that in addition to using a sufficient number of swarms to create a large enough swarm to threaten the whole party and have multi attacks that I would add some special abilities for tiny creatures. First, I'm thinking that tiny creatures can ignore worn armor. Natural armor, or magic armor like mages armor, or bark skin would have full effect, but plate mail, magical or now, would offer no protection against a swarm of ants, bees, spiders, etc. Further, anyone in plate, or chain, will have disadvantage on attacks against the swarm attacking them unless they doff their armor.

Maybe that seems unbalanced, but it would make swarms worthy of fear and more interesting.

Other things to make mobs and swarms more interesting and challenging:

• Give disadvantage to perception checks when engaged in combat with mobs or swarms
  
  
• Make communication among the party more difficult with din of a mob battle or the noise of a swarm. If you want to yell or hand-signal a command to another player, you have to make a CHA (performance) check to make your message heard/seen and understood. It would still be a free action. If in a swarm of tiny creatures, make a saving throw or have your mouth filled with the creatures and take a level of exhaustion as you choke on them (or if that's to harsh, a disadvantage on all attacks, skill checks, or saves for the next round.

I'd be interested in learning other tips for running mobs and swarms in 5e.

Like zombie hordes or orc war camps, I've found my best success using swarms has been as a hazard/obstacle to be dealt with, navigated, or circumvented through clever play, rather than than a monster to kill. Similar to how 5e translated the green slime as a dungeon hazard – rather than a monster – I think a similar approach to swarms makes a lot of sense.

I haven't written this down before, but my approach looks a lot like this (using an actual play example)...

Swarm of Aquatic Centipedes
A massive swarm of undulating writhing centipedes clings to the walls and ceiling of this chamber with an underground pond. These particular centipedes glow 5-ft dim light when in darkness, in hues of neon green, purple, and orange, due to their phosphorescent diet. They are indifferent unless disturbed (e.g. PC climbing walls), harmed, or the caverns carved from the bowels of the dead dracolich become flooded or drip with acid (related to the story). Once they become hostile, use the following rules:

The swarm acts on three randomly determined initiative counts, each determined by rolling a d20. When it acts, a mass of centipedes crawls over a randomly character in the chamber (including PCs in the water or flying/levitating PCs which centipedes drop down onto). The character must make a DC 11 Dexterity save or take 10 (4d4) piercing damage, or half as much damage on a successful save. A creature reduced to 0 hit points by the swarm is stable but poisoned for 1 hour, even after regaining hit points, and paralyzed while poisoned in this way. Any character wielding open flame has advantage on their Dexterity save against the swarm, which has an aversion to fire.

Additionally, any PC moving across the walls or swimming through the water must make a DC 11 check (could be Athletics, Acrobatics, or Stealth, depending on what player attempts) to avoid agitating the centipedes. Each time the centipedes are agitated, they force the agitating PC to make a DC 11 Dexterity save as above, and then the damage the swarm deals increases by +1d4 for the rest of the encounter (up to a maximum of 8d4).

An unconscious and poisoned/paralyzed PC who falls into the water automatically fails one death saving throw on each initiative count of the swarm as swimming centipedes swarm the victim (though will not be further targeted by Dex saves).

Any area effect spell, thrown lantern, similar burst effect, or enchantment spell targeting multiple beasts will kill / frighten / pacify one-third of the centipede swarm, causing the swarm to lose its lowest initiative count. Three such spells or effects eliminate the threat posed by the swarm. Clever spellcasting, skill checks, or bardic music might also be able to slowly pacify the swarm, reducing the damage it deals at the DM's discretion, and if damage is reduced to 0d4 then the swarm is no longer hostile.

 

[Undrave]

Interactive environments make things always more fun

 

[Bupp]

I've used a swarm of orcs, but just used hill giant stats. Multiattack allows you to swarm two characters, and the higher bonus to hit makes the attacks more likely to land. Instead of describing it as a single hit, just describe it as multiple attacks getting in.

 

[Blue]

An idea I wish I had thought of but had read here was someone giving swarms Legendary Actions to represent the multitude of creatures that make it up. So it's acting on other initiatives as well.

 

[Garthanos]

More: Perhaps after being disbanded a swarm might sometimes leave stragglers or tenacious zealots, like if you had a swarm of 20 orcs (a small platoon) and it disbanded after losing enough hit points for 5 to have been killed you might have 2 to 4 individual orcs left behind who would then create a different scenario for the battle. One of which could be the sergeant class leader.... this would make the 20 orcs platoon in experience points like 7-9, 800 I think if I understand correctly. ( this assumes offensive ability is also translated right)

One could have formations the platoon can shift into a couple of ideas.
A closed formation prevent enemies from moving through their space
An open formation makes a swarm less vulnerable to area attacks and allows it to do that hazard duty.

Going whole hog, one might elevate swarm mechanics to be more like Chainmail

 

[NotAYakk]

So legendary actions instead of extra turns because extra turns act strangely with many spells; they deal damage at a start of a creature's turn, for example.

A legendary action of "move your speed and make an attack" works. It could even ignore OAs.

The trick is that legendary actions become part of the monster's damage budget. They spread the damage over time, which makes them far less swingy.

 

[Immoralkickass]

The one reason i hate swarms is that it counts as one creature. You have a magic item/ability that grants bonuses per creature killed? Nope, a swarm of bees counts as one bee.

 

[Jediking]

I enjoy using low level creatures through a campaign, and use a pretty simple formula to convert them into a mob using the swarm trait as a template. I usually give ranged attacks a type of Volley to increase the threat and deal consistent damage.
Take the standard goblin. CR 1/4, AC 13 (w/ shield = 15), HP 7. Attack = +4 to hit, 1d6+2 dmg (shortsword or shortbow)

To make a mob of (4) Goblins, take the standard Goblin statblock and apply the following:
-Increase it's area size by +1. Both small and medium creatures take up 1 square, so both are bumped to Large.
-Keep any traits/skills/senses that make sense. In this case, Nimble Escape allows Disengage as a bonus action. Hide as a bonus action may work in some cases, but DM can call that as it comes up.
-Add Swarm trait: a [size] swarm of Small humanoids. Can occupy another's space, can't regain HP or gain THP.
give it resistance to bludgeoning, piercing, and slashing damage. Usually I give advantage vs spells like Hold Person or Charm Person, but do what makes sense for you
-Multiply the HP by 2 (this takes into account the resistance)
-Double the damage dice to half the number of creatures in the swarm.
--For melee attacks they have advantage against any creature who is occupying the same space.
--For ranged attacks, the target instead makes a Dex save or take dmg, or half on a success.

Mob of Goblins
Large swarm of Small humanoids (goblinoid)
AC: 13 (15 w/ shields)
HP: 14
Resistances: bludgeoning, piercing, slashing
Swarm: can occupy other creatures spaces, cannot regain HP or gain THP
Nimble Escape: can take Disengage or Hide as a bonus action
Pack tactics: has advantage on melee attacks against any creature occupying its space.
Actions:
Shortswords: +4 to hit; 2d6+2 P
Shortbows: target must make a DC 12 Dex save or take 2d6 piercing, or half on a success.


Now you can run 16 goblins as 4 swarms, which is easier to manage in combat.
Or do this again, and have a Huge mob of 8 Goblins.
Or again, and suddenly a Gargantuan horde of 16 Goblins is tearing through a town, filling the skies with a volley of arrows to deal 8d6 in a 10 ft radius to.