According to Mckenna Grace, it was somewhat more difficult (at least for her) to work with the surviving original cast compared to Ghostbusters: Afterlife (2021) where the original actors came in late in the film and were only on set for 2 weeks to shoot the climax. In this installment, the original cast were on set for about 90% of the shoot. Grace admitted that while it was fun working with them and hearing their stories, she also felt a little intimidated and worried about screwing up in front of the guys who started this whole thing 40 years ago.
When Nadeem asks if anyone has a lighter, Ray replies that he stopped smoking in the 90s, whilst this may be a burden to their current predicament, it's a call back to Ray's bad habit, where he can be seen smoking throughout Ghostbusters (1984) and smoking a cigar in Ghostbusters II (1989).
The scenes in which Trevor attempts to catch Slimer are similar to a subplot that was filmed for Ghostbusters II (1989) but ended up being cut. In that deleted subplot, which also took place inside the Ghostbusters HQ and was supposed to be a running gag in that film, Louis Tully tried to catch Slimer on several occasions but failed. He also tried to bait him into a trap with food, something that Trevor does as well.
Ghostbusters: Frozen Empire is dedicated to the late Ivan Reitman, the original director of the first two movies who passed away on February 12, 2022.
When Gary says he picked out a film for movie night, he holds up a VHS copy of Cannibal Girls (1973). This was the second feature film directed by Ivan Reitman who directed the first two "Ghostbusters" films. He's also listed as a producer on this film which is dedicated to him. The title "Cannibal Girls" can also be seen on a movie theater marquee in both Ghostbusters II (1989) and Ghostbusters: Afterlife (2021).