This adversary can be spotlighted up to 2 times per GM turn. Spend Fear as usual to spotlight them.

Start with two Swarm tokens. Add one token every time this adversary is spotlighted. There can never be more tokens than current HP.

Move up to Far range, Mark a Stress to also move two allies within Close Range of your starting location.
Then, apply Spotted to one character in Close Range for everyone that moved.

Spend a Fear and remove any number of Swarm Tokens. Spawn a Tier 1 Horde with that much HP, or that many Tier 1 Minions in Close range of the Swarm Host.

Spend a Fear to spotlight up to 4 allies in Far range. They deal half damage while spotlighted this way.

Start a Countdown (8) when first spotlighted, ticking down on every action from it or its allies. When the countdown reaches 0, make a single attack against all characters in Far range. Targets you succeed against take standard attack damage and trigger Target Analysis.

When the Swarm Host or an ally under its control attacks a target in Far range, apply Spotted. If the target is already Spotted and the attack succeeds, add 1d8+2 Magical damage to the total. The Swarm Host clears a Stress or gains a fear.

Spotted characters cannot be Hidden from the Swarm Host or its allies. It is removed when that character takes damage or succeeds on a Finesse Action Roll against the Swarm Host's difficulty.