You transform up to ten bats, rats, or ravens, three quippers, five insects, or one poisonous snake within range into swarms of shadowy replicas for the duration. Each creature becomes a swarm, as described in the monster manual.
Each creature obeys your verbal commands, and in combat, they act on your tum each round. The DM has the statistics for these creatures and resolves their actions and movement.
A creature remains a swarm for the duration, until it drops to 0 hit points, or until you use an action to dismiss the effect on it.