The Spirit Slaves were specters from the ghost world used by Edward Kirilian to steal several objects needed to complete a machine that could open a portal to the ghost world.
Edward Kirilian had believed that he could control spirits and make them his slaves. After losing his job at a university, Kirilian perfected his Collars of Obedience and enslaved a few dozen ghosts.  The ghosts were ordered to steal The LB-7 laser prototype from Bright Wave High Tech Industries, a Toltec Skull from a paranormal exhibit, and a second Toltec Skull from a private collector in New York City. Once the portal the Netherworld was opened and Egon Spengler sabotaged Kirilian's machine, the Spirit Slaves began to go through, almost in relief. The last of the slaves grabbed Kirilian and took him through the portal.
- Long Orange haired one eyed green ghost with brown pants
- Brown-grey tone ghost with a cyan tank top and blue pants
- One eyed Red/Magenta color muscler ghost with a purple tank top
- Winged yellow creature (Only seen in first encounter in the tunnels)
- Linky blue ghost with a stock like top half of the head
- Linky red bug-like creature
- Big mouthed yellow
- Three eyed flying yellow beast
- Red Haired with a dark Mask Slave (Only can be seen carrying machinery with two other slaves)
- One eyed skin colored humanoid with white hair and a yellow tank top
- Dark Gray bulky humanoid with a rat like head
- Military green humanoid with black long hair (Only seen carrying placing trunk full of collars in lab)
- Spiney (Gateway Ghost)
- Lizard (Gateway Ghost)
- Flyer (Gateway Ghost)
- Eyeball (Gateway Ghost)
- ↑ Edward Kirilian (1997). Extreme Ghostbusters- Heart of Darkness (1997) (DVD ts. 16:38-16:40). Sony Pictures Home Entertainment. Edward says: "I have only a few dozen ghosts at my command."