He was a childhood friend of Kylie Griffin, but he fell under the influence of the Grundel and then he disappeared. Ten years later a creature that is like a Grudel which the Extreme Ghostbusters confront. Kylie and Roland interrogated the first Grundel about what happened with Jack and learned from the Grundel that Jack had not diverted back to his original form due to a special cocoon he was kept in. The Grundel was able to influence the nearby brother of Roland, Casey, to release him from the Containment unit. Immediately after his escape, the Grundel teamed up with Jack and went after Casey in an attempt to trap Kylie. The Ghostbusters got there just as Casey had transformed. While the rest of the team went after Jack and Casey, Kylie stayed behind and faced the first Grundel herself. Though she was unable to beat him, Roland came in and caught the Grundel in a proton stream, giving Kylie the time she needed to set the trap and re-capture the escaped ghost. Jack became human again.
She was a childhood friend of Jack, and she seems to care about him as shown all throughout the Grundelesque episode.
- "Grundelesque" -Jack at first was thought of as the Grundel, however Kylie soon finds out that the real Grundel is in the Containment Unit and that is her friend Jack.