The Darkstalker Files
The parasitic demon species that infect and produce Warlocks, kreeps resemble a large larva-like insect when in their natural form. Once they have bonded with a human, however, they dissolve into a jell-like state allowing it to permanently merge with their host and influence the host’s body and mind.
Kreeps are commonly found around cracks in the veil, syphoning Mana from inhabited dimensions in much the same way deep sea creatures can be found leaving near hydrothermal vents at the bottom of the ocean.
Kreeps are usually too small and weak to break through the veil on their own, though fissures have been formed by large numbers swarming together increasing pressure on a weak spot. Due to their diminutive size, they favor trickery and coercion to form pacts with host rather than forced possession.