Enslavers

The Enslavers are a race of other-dimensional psychic alien jellyfish from the Immaterium. Enslavers will mind control any unprotected psychic being that they can in order to turn them into living warp portals that more Enslavers can enter the material universe through. This control appers to be psionic in nature. The Enslaver Plague forced the C'tan Star-Gods to hide from them, as psionics (and the Warp itself) are lethal to them.