May 18, 2016

Rules Variant: Dangerous Swarms

Variant Rules
Comments from the Thumb: It occurred to me the other day while building a dungeon that swarms aren't particularly threatening. Sure, maybe they're scary and annoying, especially to low level players, but let's look at the rules. We'll go with a swarm of insects for this example.

Puny Bugs

The swarm of insects has 22 HP and an AC of 12. While they are resistant to weapon damage and immune to just about every condition in the book, they're still no match for any one character over about level 2. Just a few swings of the barbarian's axe and they're mincemeat. The rogue can even sneak attack them! Imagine this: thousands of itty-bitty spiders are descending upon the party. The rogue steps up to bat. We'll assume they get sneak attack. A few slashes of a dagger and all 8436 (roughly estimated) spiders are dead.

What. What even.

A swarm should be easy to barbecue via fireball or the like, but nigh-impossible to melee to death unless you have a giant flyswatter, especially for swarms of insects. Have you ever tried to swat a fly out of the air? Try it with a sword. You have a few options here if you want your swarms to continue to be threatening at higher levels.

Variant 1: More Threatening Swarms

The first option is to beef up the swarm. Higher AC or HP is the simplest route. Maybe give them a trait that doubles their resistance, making attacks do 1/4 damage. For insect swarms, I might even make them outright immune to piercing and slashing. Definitely make them vulnerable to non-weapon damage to compensate though (fire, cold, lightning, acid, poison, force, thunder, etc.).

Variant 2: Swarms as Hazards, Not Enemies

Your next option is to ditch the stats altogether. The DMG contains rules for dungeon hazards. Do something like that. Here, I'll take a crack at it, once again using the swarm of insects. For fun, we'll use centipedes.

Centipede Swarm
A swarm of centipedes typically covers a 5 foot square, has 10 hit points, an AC of 12, and is immune to nonmagical bludgeoning, slashing, and piercing damage. When a creature moves within 5 feet of the swarm for the first time or starts its turn there, the swarm immediately moves to occupy the creature's space, and the creature must make a DC 12 Dexterity saving throw. On a successful save, the creature becomes aware of the swarm if it wasn't already, and suffers no further effects. On a failed save, the creature takes 1d6 piercing damage as the centipedes begin to climb all over its body and bite it. The centipedes then move with the creature until they are removed or destroyed.
     At the start of the creature's next turn and every turn thereafter, it can use its action to make a DC 15 Dexterity saving throw. On a success, the creature shakes the centipedes off and the effect ends. On a failure, the creature takes another 1d6 piercing damage and 3d6 poison damage, and is poisoned for the next minute. A centipede swarm that is reduced to 0 hit points is instantly destroyed. The swarm can also be removed by jumping into water or similar methods, at the DM's discretion.

One thing to note: as with everything in D&D, you can adjust all of the swarm's stats to make it harder or easier for your party. Feel like the saving throw DC is a bit low? Want the damage to be a bit higher? Maybe give it vulnerability to fire, cold, acid, etc.? That's your prerogative. You can also replace the centipedes with any other poisonous creepy crawly.


  1. I'd change a few things:
    1. Immunity to all piercing
    2. Resistance to all slashing and bludgeoning
    3. A trait that halves damage from single-target attacks (worded as 'attacks and spells that specify a creature or creatures as their target')

    This way:
    1. You can't stab a swarm, even if you have a magic dagger.
    2. Cutting or smashing a swarm isn't very effective, even if you use magic to hurl pebbles.
    3. AoE is the only effective way to deal with swarms.

    Optionally, there are some other rules that could be fun to add:
    -Make swarms a size or two larger and give them a variant of the trait that ochre jellies have.
    -Some interaction with bright light.
    -Bonus damage against prone creatures.

    1. All really good ideas. I think I'll publish a few finalized stat blocks in a future update.

  2. I really like this variant rule. In fact, I think that this is more of a fix than a rule change. Swarms were utterly useless, and I've never used them because they never posed a legitimate threat to anyone, except level 1's of course, because a goat can kill a level 1(seriously, it's happened before.) This is a great idea, and I will be shamelessly stealing it to use it in future campaigns.

    1. Yeah, 1st level characters are laughably squishy. I had a level 1 character who got killed by an alley cat once, back in the days of 3.5.

  3. First level characters are the reason i make multiple characters.

    You could use the stomp action against creepy crawlies and swat/slap against flighty crawlies. My favorite swarms are leeches. Does 1 hp dmg per round until satiated then add 1 hp poison dmg per round until it releases. Usually 3 to 5 per character and does 2hp dmg on removal. Stick on for 3 to 5 rounds.

  4. I think that for flying swarms it would make sense to have a damage cap from mundane damage types (slashing/piercing/bludgeoning) to reflect only managing to hit a few of the flies or whatever they are. It doesn't make a lot of sense for them to do more than 1 damage to a PC, especially at higher levels, but it makes sense for them to apply diseases, poison, or similar conditions.

    Unless magically enhanced, I don't see them being much more than a flavourful addition to an encounter for most PCs.

  5. perhaps give the swarms about 10-20 hp, but make every slashing or piercing attack deal only 1 damage?

  6. So. A level 4 Craftsman can churn out 73000 gold in a year if they have consistent buyers?

    1. I personally am making it 10g per level instead of 50. *Nods* Unless someone can explain to me how someone can churn our 13 longsword a day.

    2. Sooooo in the wrong comments lol