Swarms Galore

Insects swarm together from the ground behind an unsuspecting party. Their rear guard has not noticed the insects crawling along the ground. They take off into the air and move as one, taking the party by surprise. Biting, scratching, and tearing through the flesh of their enemies, this swarm consumes the party in no time, leaving behind clean, white bones. Hopefully, this will attract many more unsuspecting parties to the area. This swarm is hungry.

Move as one. Swarms move as one. They act as one. They move and exist as one. They attack as one. However, they can be weakened. And when weakened, they are weakened as one.

Swarms have often been of interest to scholars as they are at the heart of most plagues and civic disasters. Their potential is unlimited as they become larger and larger in size.

Strength in Numbers. The more the merrier when it comes to swarms. A swarms strength comes from the ammount of creatures. Each creature in the swarm brings something to the table.

The HP of each swarm is defined by a number of creatures. For example, a Swarm of Rats has 24 HP, and as a medium swarm of tiny beasts would approximately have 50 rats. Each rat would represent 1/2 HP.

An attack also represents a percentage of creatures that are able to make contact with the target creature. For example, a Swarm of Rats deals 7 (2d6) damage per attack. This means approximately 7 rats were able to make contact with either their claws or teeth.

Other Key Features. Swarms have the unique ability to fit into any space. They can occupy larger spaces as well as smaller spaces. They are able share spaces with other creatures, including those they are attacking.

Variant: Damamge Vulnerability: Area Damamge. If affected by an area effect spell, a swarm takes double damage. For example, a fireball would more adequately effect a swarm of creatures than a chromatic orb will as the swarm is absorbed in entirety of a fireball.

Any Animal Might Swarm.

Birds of a feather stick together. If a creature feels the need to swarm it can and will. And while some animals are less likely to swarm consider reasons they may feel the need to. Bears may swarm, as they flee a forest fire. Multiple types of beasts could appear in a swarm of animals fleeing a forest fire. Because of this here are some rules for creating a swarm of beasts.

Why is just as important as what. When creating a swarm of beasts it is just as important to know the reasoning behind the swarm. A swarm moves as one unit. This is not something easily achieved for animals with an average Intelligence of 1. So remember the reason for the swarm.

A swarm is more than just a number of the same beast. A swarm of 50 rats opperates differently than 50 rats would in battle. Considering this look at what each attack, hit point, and AC point are represented by. And make sure to adjust accordingly. You do not simply want to make a swarm of cats, and say that it is 50 cats if it is only as big as medium swarm of tiny beasts.

Mixing beasts. As in the example of the forest fire, there may be times that varried beasts swarm. To keep this simple consider opperating two swarms. One of small beasts and smaller. Another of medium beasts and larger. They have the ability to occupy the same space but this would make things easier for adjusting attacks, HP, AC, and CR.

CR. If it seems too challenging it may just be that. You can always downpower a swarm mid battle by halving its hitpoints. Give the player with the highest passive perception a critical on their next attack for noticing the queen bee - halving the HP. Find a way to adjust the damage output or hit points in battle that makes sense and follows a story.

Remember the number one rule: Have fun. Dungeons and Dragons is meant to be a game of fun. If you find you're too wound up trying to make every swarm encounter just perfect, then do what feels natural. Follow a path that works for you and your players. Have fun.