Yellow Slime (also known as Yellow Ectoplasm) 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 Game
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.
Loftur Þorsteinsson was drenched in Yellow Slime by the Gulper Ghost after it was released by Egon Spengler. In a different universe, Patty Tolan and Jillian Holtzmann were covered in Yellow Slime after the latter blew up a ghost named Ralph. The 101 pilot team, consisting of Cait Banner, Evan Torres, Zoe Zawadzki, and Garrett Parker, were exposed to the slime when an open portal was closed on the Bronx Spook's appendage.
Yellow Ectoplasm is a mild form of Psychomagnotheric Ectoplasm. A ghost suffering from the equivalent to emotional stress is more likely to leave behind Yellow Ectoplasm. It does cause some mild psychotropic effects but the transfer isn't one to one. A person slimed by a frightened ghost will not become frightened. However, any emotion a person is already feeling may be temporarily amplified.  The Draugar were witnessed to leave it behind. While covered in it, Janine Melnitz kissed Egon Spengler on the lips. She expressed surprise and admitted she shouldn't have kissed him but she was just happy to see the Ghostbusters had returned after being missing for months.
- Ongoing Series
- Ghostbusters 101
- Ghostbusters Annual 2018
- 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
- Ghostbusters 101 Class Notes (2017). IDW Comics- "Ghostbusters 101 #3" (2017) (Comic p.24). Ghostbusters 101 Class Notes reads: "A ghost suffering from the equivalent to emotional stress is more likely to leave a yellow-hued ectoplasmic discharge. While nowhere as potent as the pink stuff, yellow ectoplasm does cause some mild psychotropic effects, but they aren't 1:1. Being slimed by a sufficiently frightened ghost isn't going to transfer that emotion to you, but the yellow slime may temporarily heighten any emotion you're already experiencing."