Excerpts: Swarms

Well, the release of the new game is right around the corner, so it's time to blow the lid off this thing. Since 4E was first announced, gamers have besieged us with phone calls, emails, and even a protest march demanding one thing above all else: How do swarms work in 4E?

Well, the day is at hand. We're about to pull back the curtain on what might be the greatest stride forward in swarm design known to mankind. But first, how did we end up in this glorious state?

Well, swarms are cool, but researching how we think swarms might actually work into D&D was not so cool. For this, we locked a designer in a sealed box with 100,000 ants. We threw rocks at hornets' nests, drop kicked beehives, and stuck our hands into crates of scorpions. From these experiences, we drew the following conclusions:

Oh my god, insects can sting.
No, seriously. That HURTS.
We decided that any of those feats were more fun than the 3E swarm rules.
The 3E swarm rules fell into the trap of simply trying to model reality as we know it, from movies, comics, or the real world. That might be a great move if you want to build a simulator, but it isn't so hot for a game. Instead, we wanted rules that were evocative. You should feel like you're fighting a swarm, but that feeling should be less like boredom and more like "GET THESE THINGS OFF OF ME."

So, a few highlights about 4E swarms:

Swarms are hard to hurt. Hacking at a pile of bugs with a sword is inefficient, but it's also scary to face a monster that's hard to hurt. The swarm marches on in a relentless wave. We liked that feel, and we could easily set the swarm's hit points to balance the effect.
They're hard to push around, again to make them feel relentless.
They can go almost anywhere. Closing a door doesn't do much to slow down a swarm. The bugs simply crawl under it, or through the cracks in the door's frame.
Originally, a single swarm "monster" was four Medium size groups of creatures. They worked similarly to minions, but the effect on the table was disappointing. Swarms didn't feel like tides of hungry critters, more like disposable bags of hit points. We tried toughening them, but that worked against the 4-for-1 discount they offered. In the end, we dropped the split and worked to simplify and streamline our existing rules.

So, now the swarm piece of the 4E puzzle has fallen into place. 4th Edition is right around the corner, and with it endless waves of hungry bugs, drakes, and other nasties.
--Mike Mearls

From the Monster Manual Glossary:

Swarm: A swarm is considered a single monster even though it is composed of several Tiny creatures. Most single swarms are Medium, but some can be larger.

A swarm takes half damage from melee and ranged attacks. It is vulnerable to close and area attacks, as indicated in the monster’s stat block.

A swarm is immune to forced movement (pull, push, and slide) effects from melee and ranged attacks. Close or area attacks that impose forced movement affect the swarm normally.

A swarm can enter or move through an enemy’s space; this movement does not provoke opportunity attacks. An enemy can enter a space occupied by a swarm, but the space occupied by the swarm is considered difficult terrain, and doing so provokes an opportunity attack.

A swarm can squeeze through any opening large enough to accommodate even one of its constituent creatures. For example, a swarm of bats can squeeze through any opening large enough for one of the bats to squeeze through. See the Player’s Handbook for squeezing rules.

Drake

Needlefang Drake Swarm
Savage marauders the size of cats, needlefang drakes swarm over their victims, pull them to ground, and strip them to the bone in seconds.

Needlefang Drake SwarmLevel 2 SoldierMedium natural beast (reptile, swarm)XP 125Initiative +7Senses Perception +7
Swarm Attack aura 1; the needlefang drake swarm makes a basic attack as a free action against each enemy that begins its turn in the aura.
HP 38; Bloodied 19
AC 18; Fortitude 15, Reflex 17, Will 14
Immune fear; Resist half damage from melee and ranged attacks;
Vulnerable 5 against close and area attacks.
Speed 7
Swarm of Teeth (standard; at-will)+8 vs. AC; 1d10 + 4 damage, or 2d10 + 4 damage against a prone target.Pull Down (minor; at-will)+7 vs. Fortitude; the target is knocked prone.Alignment UnalignedLanguages —Str 15 (+3) Dex 18 (+5) Wis 12 (+2) Con 14 (+3) Int 2 (-3) Cha 10 (+1)
Needlefang Drake Tactics
Incited by hunger, needlefang drakes fearlessly rush toward their prey, knock it prone (using pull down), and use their swarm of teeth to feast upon it.

Stirge

Stirge Swarm

Stirges are bloodsucking, bat-like horrors that lurk in caves and ruins. Lone stirges are little more than pests and nuisances—but they are rarely encountered alone. Stirges tend to gather in large flocks that can exsanguinate an adult human in a matter of minutes.

Stirge SwarmLevel 12 BruteMedium natural beast (swarm)XP 700Initiative +9Senses Perception +6; darkvision
Swarm Attack aura 1; the stirge swarm makes a basic attack as a free action against each enemy that begins its turn in the aura.
HP 141; Bloodied 70
AC 24; Fortitude 21, Reflex 24, Will 23
Resist half damage from melee and ranged attacks;
Vulnerable 10 against close and area attacks
Speed 2, fly 6 (hover)
Bloodsucking Swarm (standard; at-will)+15 vs. AC; 2d6 + 4 damage, and ongoing 5 damage (save ends).Alignment UnalignedLanguages —Skills Stealth +14 Str 8 (+5) Dex 16 (+9) Wis 10 (+6) Con 11 (+6) Int 1 (+1) Cha 4 (+3)
Stirge Swarm Tactics
Stirge swarms gave rise to the old dwarven saying: “I don’t have to outrun the stirges, I only have to outrun you.” A hungry swarm will chase its prey for miles, if need be.