Harold Ramis will appear

Although the actor passed away in 2014, Harold Ramis will still have a part in the movie. 

Using archival footage, Harold's Egon Spengler will appear as a CGI ghost, having first done so in the previous movie.

Reflecting on their work on bringing Harold back for the 2021 movie, VFX artist Sebastien Raets from MPC said: "Respectfully bringing Harold Ramis back to the screen was a project we were honored to take on, and we were humbled and overjoyed with the positive response from the client, the audience and Harold’s family.”