Yellow Slime is a strain of Ectoplasm. The Cult of Gozer synthesized a strain of Yellow Slime from Black Slime. A (super)naturally occurring strain, different from the Cult's version, has been observed to be emitted by Draugar. 
Ghostbusters: The Video GameEdit
In the 1920s, the Cult of Gozer experimented in creating new strains of Ectoplasm. One such strain was Yellow Slime but its abilities were never demonstrated and was stored in the Slime Laboratories on Shandor Island. 
After the Grendel was trapped by Janine Melnitz, she was admonished by one of the Draugar. Coincidentally, the interdimensional tear created by the Ghostbusters opened upon the ghost and it imploded. Yellow Slime rained down on Janine, Ron Alexander, and Special Agent Melanie Ortiz. Later in the summer, Janine suddenly became catatonic and discharged Yellow Slime from her eyes. After Roger Baugh returned with Egon Spengler, Janine was completely encased in the slime and was floating in mid-air. Positively charged pink slime and Gris-Gris had no effect on the Yellow Slime. Once the Draugar released their hold, the Yellow Slime on Janine vanished.
- ↑ Egon Spengler (2013). IDW Comics- "Ghostbusters Volume 2 Issue #5" (2013) (Comic p.17). Egon Spengler says: "Where did that Yellow Slime come from?"
- ↑ Ghostbusters: The Video Game - Slime Laboratories Reference