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5E Urgent, for tonight's game: Making a Swarm


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robus

Lowcountry Low Roller
Supporter
These days I would use GiffyGlyph’s Monster Maker and just pick the challenge level I want, plug in the stats and then describe the monster as a swarm of whatever.
 


prabe

Aspiring Lurker (He/Him)
Supporter
The Midgard books have a few monters as swarms and as individuals, IIRC, and the Monster Manual Expended has a swarm of stirges that might serve as a basis of comparison if nothing else.
 

DMMike

Game Masticator
For 5e, just a few easy steps:

-Start with your base creature.

-Expand its size based on number of creatures and their required combat spacing. Other characters can enter this space.

-Multiply hit points by the number of swarm members.

-The swarm gets advantage (on pretty much everything) if its target is within its space. Disadvantage on anything without.

-Every PC in the swarm fights against the stats of the base creature, but does damage to the collective hit point pool.

-At 50% hit points, the swarm disperses. Stragglers (maybe the leaders/big guys) remain.

I think that covers everything...
 

jgsugden

Hero
Quick and dirty modifications that work for most low level beasties and humanoids.

  • Start with a single version of the creature.
  • Increase the size category by 2 (tiny to medium, small to large, medium to huge).
  • Double the hit dice and then add 5 hit dice.
  • Add 6 to the strength. This may impact attack bonuses and damage.
  • Give it bludgeoning, piercing and slashing resistance.
  • Give it charm, fright, grap, paralyze, petrify, prone, restrained, and stun immunity
  • Give it the swarm ability.
  • Add 2d6 to the damage of the creature. If the creature is now large or bigger, give it (or modify) a multiattack action allowing 1 extra attacks.
  • If it can cast spells or uses an ability that operates like a spell, give it 2 swarm actions (which are essentially legendary actions) that allow it to use the ability or spells at the end of another creature's turn. Quadruple any available uses or spell slots.
  • Generally, increase CR by 3 levels (1/4 -> 1/2 -> 1 -> 2, 1 -> 2 -> 3 -> 4). Compare to existing monsters to fine tune.

Swarm of Bandits
Huge swarm of medium humanoid (any race), any non-lawful alignment

Armor Class 12 (Leather Armor)
Hit Points 49 (9d8 + 9)
Speed 30 ft.

STR
17 (+3)
DEX
12 (+1)
CON
12 (+1)
INT
10 (+0)
WIS
10 (+0)
CHA
10 (+0)

Senses Passive Perception 10
Languages Any one language (usually Common)
Challenge 1 (100 XP)

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium humanoid. The swarm can't regain hit points or gain temporary hit points.

Actions
Multiattack. The bandit swarm may make 2 attacks with any combination of scimitar or light crossbow attacks.
Scimitar. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 13 (3d6 + 3) slashing damage.
Light Crossbow. Ranged Weapon Attack: +3 to hit, range 80 ft./320 ft., one target. Hit: 12 (1d8 + 2d6 + 1) piercing damage.
Swarm of Drow
Huge swarm of medium humanoid (elf), neutral evil

Armor Class 15 (Chain Shirt)
Hit Points 49 (11d8)
Speed 30 ft.

STR
16 (+3)
DEX
14 (+2)
CON
10 (+0)
INT
11 (+0)
WIS
11 (+0)
CHA
12 (+1)

Skills Perception +2, Stealth +4
Senses Darkvision 120 ft., Passive Perception 12
Languages Elvish, Undercommon
Challenge 1 (100)

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium humanoid. The swarm can't regain hit points or gain temporary hit points.

Fey Ancestry. The drow has advantage on saving throws against being charmed, and magic can’t put the drow to sleep.

Innate Spellcasting. The drow’s spellcasting ability is Charisma (spell save DC 11). It can innately cast the following spells, requiring no material components:
At will: dancing lights
4/day each: darkness, faerie fire

Sunlight Sensitivity. While in sunlight, the drow has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.
Actions

Multiattack. The drow may make 2 attacks with any combination of scimitar or hand crossbow attacks.
Shortsword. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 13 (3d6 + 3) piercing damage.
Hand Crossbow. Ranged Weapon Attack: +4 to hit, range 30/120 ft., one target. Hit: 5 (3d6 + 2) piercing damage, and the target must succeed on a DC 13 Constitution saving throw or be poisoned for 1 hour. If the saving throw fails by 5 or more, the target is also unconscious while poisoned in this way. The target wakes up if it takes damage or if another creature takes an action to shake it awake.

Swarm Actions
The swarm can take 2 swarm actions, choosing from the option(s) below. Only one swarm action option can be used at a time and only at the end of another creature's turn. The swarm regains spent warm actions at the start of its turn.

Spellcasting. The swarm may cast a spell.
 

Oofta

Title? I don't need no stinkin' title.
I like @jgsugden suggestion, another option is to use the mob rules from chapter 8 of the DMG. Basically take their damage and determine how many monsters will hit on any given turn.

The example they give: eight orcs surround a fighter. The orcs’ attack bonus is +5, and the fighter’s AC is 19. The orcs need a 14 or higher to hit the fighter. According to the table, for every three orcs that attack the fighter, one of them hits. There are enough orcs for two groups of three. The remaining two orcs fail to hit the fighter.

Mob Attacks
d20 Roll NeededAttackers Needed for One to Hit
1–51
6–122
13–143
15–164
17–185
1910
2020

I use this especially when the bad guys have ranged attacks or a mix of range and melee.
 

the Jester

Legend
I'll be happy to take a crack at it if you tell me what the base creature is and what CR you're trying for. I have a long history of making creatures into swarms, from 3e to 5e.
 

dave2008

Legend
Does anyone know of a good guide to creating swarms out of low-level monsters?
I'm not sure what you looking for, but I have some swarms in my 5e Hardcore Monsters thread:
  • Vargoulle Swarm (CR 21)
  • Imp Swarm (CR 21)
  • Lemure Horde (CR 9)
EDIT: It is pretty easy to take one of those and modify with a different monster. One thing that is different with my approach is to use Legendary actions to make them a bit more dynamic.
 
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jayoungr

Hero
Supporter
I'll be happy to take a crack at it if you tell me what the base creature is and what CR you're trying for. I have a long history of making creatures into swarms, from 3e to 5e.
Twig, vine, or needle blights; would like them to be about CR 5-6. Thanks!
 


the Jester

Legend
Okay, how do these look?

Twig Blight Swarm

Large swarm of small plants, neutral evil

Armor Class 13 (natural armor)
Hit Points 78 (12d10+12)
Speed 20 ft.

STR 14 (+2), DEX 13 (+1), CON 12 (+1), INT 4 (-3), WIS 8 (-1), CHA 3 (-4)

Skills Stealth +4
Damage Resistances bludgeoning, piercing, and slashing
Damage Vulnerabilities fire
Condition Immunities blinded, deafened
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 9
Languages understands Common but can't speak
Challenge 5 (1,800 xp)


False Appearance. While the swarm remains motionless, it is indistinguishable from an area of dead shrubbery.

Shed Blights. When the swarm is reduced to half its hit points or fewer, and again when it is reduced to 0 hit points, four twig blights appear in unoccupied spaces adjacent to the swarm. If there are no unoccupied spaces adjacent to the swarm, they instead appear in the swarm's space.

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Small twig blight. The swarm can't regain hit points or gain temporary hit points.

ACTIONS

Multiattack. The swarm makes one attack against each creature in its space, plus one attack against one other creature in its reach.

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 19 (4d8+1) piercing damage, or 10 (2d8+1) piercing damage if the swarm has half of its hit points or fewer.


Needle Blight Swarm

Huge swarm of medium plants, neutral evil

Armor Class 12 (natural armor)
Hit Points 97 (13d12+13)
Speed 30 ft.

STR 17 (+3), DEX 12 (+1), CON 13 (+1), INT 4 (-3), WIS 8 (-1), CHA 3 (-4)

Damage Resistances bludgeoning, piercing, and slashing
Condition Immunities blinded, deafened
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 9
Languages understands Common but can't speak
Challenge 5 (1,800 xp)


Shed Blights. When the swarm is reduced to half its hit points or fewer, and again when it is reduced to 0 hit points, four needle blights appear in unoccupied spaces adjacent to the swarm. If there are no unoccupied spaces adjacent to the swarm, they instead appear in the swarm's space.

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Medium needle blight. The swarm can't regain hit points or gain temporary hit points.

ACTIONS

Multiattack. The swarm makes one claw attack against each creature in its space, plus one claw attack against one other creature in its reach. Alternatively, it can make up to four needle attacks.

Claws. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 21 (4d8+3) piercing damage, or 12 (2d8+3) piercing damage if the swarm has half of its hit points or fewer.

Needles. Ranged Weapon Attack: +4 to hit, range 30/60 ft., one target. Hit: 15 (4d6+1) piercing damage, or 8 (2d6+1) piercing damage if the swarm has half of its hit points or fewer.


Vine Blight Swarm

Huge swarm of medium plants, neutral evil

Armor Class 12 (natural armor)
Hit Points 119 (14d12+28)
Speed 10 ft.

STR 18 (+4), DEX 8 (-1), CON 14 (+2), INT 5 (-3), WIS 10 (+0), CHA 3 (-4)

Skills Stealth +2
Damage Resistances bludgeoning, piercing, and slashing
Damage Vulnerabilities fire
Condition Immunities blinded, deafened
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 9
Languages understands Common but can't speak
Challenge 6 (2,300 xp)


False Appearance. While the swarm remains motionless, it is indistinguishable from a tangle of vines.

Shed Blights. When the swarm is reduced to half its hit points or fewer, and again when it is reduced to 0 hit points, four vine blights appear in unoccupied spaces adjacent to the swarm. If there are no unoccupied spaces adjacent to the swarm, they instead appear in the swarm's space.

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Medium vine blight. The swarm can't regain hit points or gain temporary hit points.

ACTIONS

Multiattack. The swarm makes one attack against each creature in its space, plus up to one attack against another creature in its reach.

Constrict. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 26 (4d10+4) bludgeoning damage, or 15 (2d10+4) bludgeoning damage if the swarm has half of its hit points or fewer. In addition, each Large or smaller creature hit and each Huge target hit in its space is grappled (escape DC 15). While grappled in this way, the target is restrained, and it moves with the swarm.

Entangling Plants. Grasping roots and vines sprout in the swarm's space and in the area within 20' of the swarm, extending around corners. These vines wither away after 1 minute. For that duration, the area is difficult terrain for nonplant creatures, and each creature of the swarm's choice within the areea when the plants appear must succeed on a DC 15 Str save or become restrained. A creature can use its action to make a DC 15 Str check, freeing itself or another creature restrained by the vines within reach on a success.
 


the Jester

Legend
Those look great! Thank you so much!
My pleasure. I hope they work well for you in play.

The whole "drop a few base creatures when bloodied and killed mechanic" has worked really well for me in modeling that these swarms are actually made of those creatures. My players have seemed to enjoy the little twist it throws into a fight, too.
 

Harzel

Adventurer
  • Add 6 to the strength. This may impact attack bonuses and damage.
  • Give it bludgeoning, piercing and slashing resistance.
Twig Blight Swarm

Damage Resistances
bludgeoning, piercing, and slashing
First, generally I think these were great answers; so really I am just nitpicking here.
But.
As a matter of verisimilitude, I would only give bludgeoning, piercing, slashing resistance if the base creature is tiny, or, perhaps, small. But maybe I'm missing something.
Not sure I understand the strength increase unless the creatures are intelligent enough and predisposed by temperament to act in a concerted fashion. (Although the swarm should just be flat immune to grappling, shoving, etc.)
 

Harzel

Adventurer
  • Add 2d6 to the damage of the creature. If the creature is now large or bigger, give it (or modify) a multiattack action allowing 1 extra attacks.
Another possibility would be to multiply the base creature damage. Off the top of my head, maybe 4x for tiny base creatures, 3x for small, and 2x for medium.
 

Harzel

Adventurer
  • Start with a single version of the creature.
  • Increase the size category by 2 (tiny to medium, small to large, medium to huge).
  • Double the hit dice and then add 5 hit dice.
Another idea: for tiny or small base creatures, you could create a megaswarm by increasing the size and hit dice. And as it lost HP, it could break apart into smaller swarms. Obviously some details to be worked out, which I would do, but a little pressed for time atm.
 

the Jester

Legend
As a matter of verisimilitude, I would only give bludgeoning, piercing, slashing resistance if the base creature is tiny, or, perhaps, small. But maybe I'm missing something.
My reasoning is based on the existing examples of swarms. They all have these resistances, even though the base creatures (e.g. a poisonous snake or rat) don't. I take this to mean that those resistances are less about the base creatures' size and more about the fact that it's a swarm containing a bunch of said creatures.

Not sure I understand the strength increase unless the creatures are intelligent enough and predisposed by temperament to act in a concerted fashion.
It's the same basic argument- swarms of poisonous snakes, quippers, and rats have Str scores of 8, 13, and 9, while the individual base monsters have Str scores of 2 each. I don't think that a swarm of snakes or rats are intelligent enough or predisposed to act in a concerted fashion. Therefore, I applied the principle that the swarm is stronger by virtue of being a swarm.
 

Harzel

Adventurer
It's the same basic argument- swarms of poisonous snakes, quippers, and rats have Str scores of 8, 13, and 9, while the individual base monsters have Str scores of 2 each. I don't think that a swarm of snakes or rats are intelligent enough or predisposed to act in a concerted fashion. Therefore, I applied the principle that the swarm is stronger by virtue of being a swarm.
Ok, interesting. I had not noticed that.
 

Do we really need swarms/ mobs?

It's not a bad idea, but even of upwards of a dozen creatures, they already all share the same initiative count, and you're basically rolling 1d20 and adding a number around +5 to it.

You could resolve all 12 of those creatures turns in under a minute, even using miniatures (possible move, roll attack, turn ends, repeat).
 

Mythological Figures & Maleficent Monsters

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