Following his retirement from ghostbusting, Egon Spengler wrote his own book, Spengler's Spirit Guide.
This book cataloged the spirits Egon encountered during his days as a Ghostbuster (and probably included material borrowed from Tobin's Spirit Guide).
Spengler's Spirit Guide is also available in CD-ROM. Users can access a database of entities through the Demon Browser. In 1997, it was currently in Version 2.1.
- Kylie read "Spengler's Spirit Guide" cover to cover six times. 
- Coincidentally, in issues of Marvel Comics Ltd's The Real Ghostbusters series, one page was dedicated to Spengler's Spirit Guide. Egon Spengler would pick a topic from fan mail and discuss such as the link between Ancient Egyptians and the spirits of the undead.
- On page 19 of Ghostbusters Volume 2 Issue #1, a copy of Spengler's Spirit Guide makes a non-canon cameo right of Wise Natural Potato Chips bag but it has the font of Pagan Rituals & Ceremonies from "Casting the Runes"
- On page 12 of Ghostbusters: Get Real Issue #3, Kylie is holding a Spengler's Spirit Guide.
- On the Ghostbusters Annual 2015 regular cover, the Spengler's Spirit Guide makes a non-canon cameo.
- "Darkness at Noon, Part 1"
- Kylie Griffin brought this book with her to Spengler's class.
- "Be Careful What You Wish For"
- "Sonic Youth"
- "Seeds of Destruction"
- Egon runs a search in the Spirit Guide database for a match based on Eduardo and Roland's descriptions of a plant ghost that turned out to be Shanbahac
- Kylie uses the Spirit Guide database on a laptop to look for the entry on the Grundel
- "In Your Dreams"
- "Eyes of a Dragon"
- "Mole People"
- The CD-ROM version's Demon Browser is used to identify the Energy and Lightning Demons in the Energy Sucking Demons category.
- Kylie Griffin (2009). Extreme Ghostbusters- Darkness at Noon, Part 1 (1997) (DVD ts. 10:45-10:47). Sony Pictures Home Entertainment. Kylie says: "I read your book cover to cover six times."
- Kylie Griffin (2009). Extreme Ghostbusters- Deadliners (1997) (DVD ts. 11:41-11:47). Sony Pictures Home Entertainment. Kylie says: "Or maybe they're the Vathek. The Spirit Guide says: "They're spectral forms who enter the realm of the living through the act of writing.""
- Kylie Griffin (2009). Extreme Ghostbusters- Be Careful What You Wish For (1997) (DVD ts. 11:49-11:51). Sony Pictures Home Entertainment. Kylie says: "I'll check the Spirit Guide database.""
- Egon Spengler (1997). Extreme Ghostbusters- Sonic Youth (1997) (DVD ts. 09:35-09:44, 10:07-10:13). Sony Pictures Home Entertainment. Egon says: "I'm guessing you didn't make it to my chapter on the Glostic Sisters. According to Irish folklore, they were a pair of wondering spirits. One was a Banshee. The other, a Siren...Banshee requires the youth of mortals to sustain her strength. Her sister is the only one who can provide it."
- Melching, Steven (1997). Extreme Ghostbusters "In Your Dreams" (Final Draft April 5, 1997) (Script p. 22). Line reads: "CLOSE ON SPENGLER'S SPIRIT GUIDE; it's open to a 17th century woodcut of MORPHEUS."
- Egon Spengler (1997). Extreme Ghostbusters- Eyes of a Dragon (1997) (DVD ts. 11:55-12:15). Sony Pictures Home Entertainment. Egon says: "The gems from the statue are known as the Dragon's Eye, they were reputed to have telekinetic properties enabling them to protect their possessor from immediate physical harm. Gu Mo twisted the power of the gems in his bid to control the 15th Flaming Circle. He was defeated when the Dragon's Eyes were used against him to lock him inside the statue."