Creep

Creeps are creatures that prey on, harass or otherwise scare young children. They are first described in the short story "Zoo Day".

Description
Creeps can be clearly seen only by children; adults almost always fail to perceive them. Even Mouse has difficulty to notice them. It is possible there is a number of varieties, but only one is described in some detail.

Haunt
Haunts are a type of creeps that prey on children's fear and terror. Children can notice them by their hosts' eyes being black and empty, which appear regular to adults. Haunts are sensible to salt and can be defeated by facing up to and conquering one's fears. They also can leave children they're parasitizing when they're sated; their hosts will never be the same as before.

Bagglers
Bagglers are a type of creep that attach themselves to adult and force them to discuss politics at any available opportunity.

"Zoo Day"
In "Zoo Day", a group of haunts attacks Margaret Angelica Dresden, who manages to defeat them, taking her first step toward recovery and healing.