A D&D 5e swarm is a type of creature that consists of many smaller creatures acting as one. A swarm can be composed of insects, rats, bats, snakes, or any other Tiny beasts.
A swarm is a challenging and versatile enemy that can overwhelm and harass adventurers with its numbers and mobility. A swarm can also be used as a hazard or an environmental feature in certain locations, such as dungeons, sewers, forests, or swamps.
A swarm has the following characteristics:
- A swarm is a single creature with a space of 10 feet, even though it is made up of many smaller creatures. A swarm can be affected by spells and effects that target a single creature, such as hold monster or dominate beast.
- A swarm can occupy another creature’s space and vice versa, and it can move through any opening large enough for a Tiny beast. A swarm cannot regain hit points or gain temporary hit points.
- A swarm has resistance to bludgeoning, piercing, and slashing damage, as well as immunity to certain conditions that affect a single creature, such as charmed, frightened, grappled, paralyzed, petrified, prone, restrained, and stunned.
- A swarm can have additional traits depending on the type of creatures that form it, such as keen smell, spider climb, or blindsight.
- A swarm can make a bite attack that deals piercing damage to one target in the swarm’s space. The damage is reduced if the swarm has half of its hit points or fewer.
SWARM TEMPLATE
- Size. Base size increases by two.
- AC. Unchanged.
- HP. Increase the amount of hit dice by 5. Increase the hit die by two steps (d1 becomes d4, d2 becomes d6, d4 becomes d8, etc. Max hit dice is 12). The modifier is multiplied by 5. E.g. A creature with 1d4-1 HP would be 6d8-5.
- Speed. Unchanged.
- Ability Scores. Add 5 to the Swarm’s Strength score.
- Saving Throws. Unchanged.
- Skills. Unchanged.
- Resistances, Vulnerabilities, and Immunities. Keeps all base Resistances, Vulnerabilities, and Immunities. Gains Resistance to Bludgeoning, Piercing, Slashing. Gains the following condition immunities: Charmed, Frightened, Grappled, Paralyzed, Petrified, Prone, Restrained, Stunned.
- Senses. Unchanged.
- Challenge Rating. Use the formula for calculating the CR found in the DMG. In general, you should expect the Challenge Rating to increase by 2 or 4 steps. For Example, a CR 0 creature might become CR 1/4 or CR 1/2 Swarm. If the Swarm would have two sources of damage from a single attack (ex. Damage from a bite that also causes poison damage), expect the CR to increase by 4 steps instead.
- Descriptor (Swarm). The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for one creature of the swarm. The swarm can’t regain hit points or gain temporary hit points.
ACTIONS
The swarm loses multiattack. It keeps all of its other actions, but single target actions have the following changes.
- To hit is increased by 2. (All Save DC’s remain unchanged).
- A Reach of 5 feet is decreased to 0 feet, and the target has to be in the swarm’s space.
- The amount of damage dice is doubled. When the swarm is at half health, it switches to the normal amount of damage dice.
- The damage die increases by two steps (d1 becomes d4, d2 becomes d6, d4 becomes d8. The damage die stops increasing at d12).
- The modifier for damage remains unchanged.
- Secondary Damage on an attack (from failing a save or something else) doubles the amount of damage dice and increase the die by two steps. This Secondary Damage remains unchanged at half health.