Jessi's Dog is the unnamed pet dog of Jessi Glaser. According to Missy, he bears striking resemblance to Nathan Fillion. His only appearance is in the episode "Sleepover: A Harrowing Ordeal of Emotional Brutality".
In "Sleepover: A Harrowing Ordeal of Emotional Brutality", Missy got a sugar rush and made out with Jessi's Dog, mistaking him for Nathan Fillion. Devin and Lola bullied her by recording her and attepmting to post it on the internet. Later, Jessi's Dog talked to Greg but it remains unclear if the dog could actually talk or if Greg just hallucinated this because he was high at the time.