Ectoplasm is a translucent goo left behind when spirit matter no longer has a will giving it form.
- Demons and other entities from the Nevernever must gather energy to themselves to take form in the mortal world; when they are destroyed or caught off from the source of their power, that matter dissolves into ectoplasm.
- Dust particles that drift through a portal between the Nevernever and the mortal realm will turn into ectoplasm.
- Magical constructs will dissolve into ectoplasm when destroyed or cut off from the conjurer's will. Mouse destroys one such construct, a giant snake created by Quintus Cassius, leaving "gallons" of ectoplasm behind.