During a botched demonstration of the Dimensionometer, Egon's soul was sucked into the Netherworld and a demon possessed Egon's body. This body was transmogrified to match the demon's but some of Egon's familiar traits were retained. The only thing he ever said was "Free to destroy!" The Ghostbusters found Egon's notes and learned they only had 15 minutes to reverse the process. However, after Peter used several canisters of tear gas, the demon was kidnapped by Helen Shreck for an exclusive interview. The demon awoke in ABS Studios and attacked everyone. Ray and Winston corralled him back to the Firehouse just as Peter returned with Egon's soul. The demon was returned back to the Netherworld.
- On page one of Ghostbusters Issue #15, the Possessor Demon is referred to on the ABS News ticker.
- On page 10 of 35th Anniversary: Ghostbusters, Egon's body is now transmogrified, similar to his animated counterpart in "Egon on the Rampage".
- Marsha Goodman (1987). Episode Call Sheet and SAG Report - "Egon on the Rampage" (1987).
- Winston Zeddemore (2009). The Real Ghostbusters - "Egon on the Rampage" (1987) (DVD ts. 10:06-10:11). Time Life Entertainment. Winston says: "And according to Egon's notes, if we don't find his soul and reverse the process inside 15 minutes, the change is permanent."