Ray's Spirit Guide is a ghost who warns Ray Stantz in his dreams.
IDW Comic Series
During a dream, that appeared to be a precognitive episode, Ray encountered a spirit guide. He warned Ray that The Third was targeting him. The guide seemed to imply this had to do with Gozer's defeat, Ray's part in choosing the Destructor Form, and destroying the Temple of Gozer.
After Idulnas succeeded in kidnapping Ray, he whisked Ray to the roof of the Shandor Building and knocked him out. The resulting blow was intended to make Ray's mind easier to influence when the re-selection of Gozer's Destructor Form began. Luckily, the spirit guide influenced Ray first and instructed him to only think of the Stay Puft Marshmallow Man, and not be swayed by Idulnas. Ray followed his advice and Gozer remained stuck in the form of the Stay Puft Marshmallow Man.
Months later, in the fall, the spirit guide appeared in Ray's dream once more. He assumed the form of Ray's romantic interest and warned him the walls of the dimensions were shifting. Annoyed by Ray's nonchalant response, the spirit guide slapped Ray and explained ghosts were 'insulation' for walls between dimensions, cracks between universes were the "other side" for everywhere, and things could be escaping. Ray took it all in and the spirit guide then advised him to start dating a real woman, maybe even the one at the doughnut shop, at the sight of his fantasy love interest.
The next year, in the summer, the spirit guide appeared in the dreams of Janine Melnitz after Egon Spengler and Roger Baugh rescued her from the Draugar.  The following spring, just before the Ghostbusters docked at Hart Island, Gozer made mental contact with Ray. Gozer chose to take on the form of Ray's spirit guide. Just as Ray caught up to the spirit guide and asked if this was important, Gozer revealed himself.
After the Ghostbusters fell victim to the Sandman, they were each placed in a dream state. Ray was stuck in a dream of going over Peter's Particle Thrower in the Firehouse only to have one of the others come into the lab and flip out. Ray was struck by a sense of deja vu. The spirit guide appeared to Ray. Ray realized they never left the Pearson house on Staten Island. The spirit guide implored Ray to keep thinking. When Ray asked him to intervene, he stated he was just a guide and had his limits. He did concede and reveal he could reconnect Ray with the others. It would be up to Ray to snap them out of their dreams and gain some control. The guide warned Ray the stakes were high as they could lose their eyes or worse. Ray understood then asked how to deal with the Sandman. The spirit guide asserted he would think of something and shoved him through a mirror. Ray ended up in Peter's dream and explained what was going on. They made their way to Winston then Egon and took on the Sandman, resulting in their liberation.
Ray's Spirit Guide has at least the ability to move about people's dreams. It is unknown what the extent to which he can manipulate the dreams to his will. He was able to inhabit the form of a person in a dream and to make the dreamer feel pain. Overall, a a guide, this entity's abilities are limited.  Against another entity tied to dreams like the Sandman, the spirit guide cannot directly intervene against him in a dream. However, if there are multiple victims, the guide can transport one victim into another victim's dream. 
- The spirit guide is visually based on the Blues Brothers character Jake Blues, who was portrayed by the late John Belushi.
- Dan Aykroyd himself had played Jake's brother Elwood on Saturday Night Live and the two Blues Brothers movies.
- John Belushi was Dan Aykroyd's original choice to play Peter Venkman.
- Slimer's excessive consumption was based on John Belushi's lifestyle, and was joking referred to as "The ghost of John Belushi" by Aykroyd himself.
- Dan Schoening did several designs for the spirit guide including Belushi's character from "Animal House," when he was dressed in a toga. 
- At one time there was a story where in the Ray's Spirit Guide was helping as an act of good faith to get the Ghostbusters' trust then eventually their help. Erik Burnham may do the story some day. 
- On page 113 of Ghosts From Our Past: Both Literally & Figuratively: The Study of the Paranormal, the inclusion of John Belushi's ghost in the case study is a nod to Ray's Spirit Guide.
- IDW Comics
- Insight Editions
- ↑ Janine Melnitz (2013). IDW Comics- "Ghostbusters Volume 2 Issue #7" (2013) (Comic p.6). Janine says: "I've been having some really weird dreams lately about this fat guy in these sunglasses."
- ↑ Ray's Spirit Guide (2015). IDW Comics- "Ghostbusters Annual 2015" (2015) (Comic p.14). Spirit Guide says: "I'm just a guide, brother. I have my limits."
- ↑ Ray's Spirit Guide (2015). IDW Comics- "Ghostbusters Annual 2015" (2015) (Comic p.15). Spirit Guide says: "Look, best I can do is reconnect you with your guys."
- ↑ Narrator (2016). Insight Editions- "Tobin's Spirit Guide" (2016) (Book p.30). Paragraph reads: "CLASS III. DOES NOT MANIFEST IN THE PHYSICAL WORLD."
- ↑ Nerdy Show Podcast 4/26/11, 36:20-36:40
- ↑ Ghostbusters Wiki Interview with Erik Burnham Part 3, Question 13 answer 12/14/15
- ↑ Interview with Andrew ShafferAndrew Shaffer says: "And Belushi's ghost was added as a nod to IDW's comic series, which uses him from time to time."
- ↑ Peter Venkman (2018). IDW Comics- "Ghostbusters Crossing Over Issue #2" (2018) (Comic p.17). Peter Venkman says: "You're like that fella in the shades that visited Ray a couple of times, yeah?"
- ↑ Narrator (2016). Insight Editions- "Tobin's Spirit Guide" (2016) (Book p.30). Paragraph reads: "We've had the opportunity to study the brainwaves of one individual contacted by a spirit guide: Dr. Ray Stantz, the coauthor of this book."