Molly is described as a mutt breed, with her most prominent traits belonging to the Irish Setter. She has reddish brown fur and stands at knee-height compared to Dave.
In the film adaption, Molly is portrayed by a male Shiba Inu. Her name is also changed to "Bark Lee". This change was supposedly made because "Bark Lee" was the given name of the actor-dog in Molly's role, and he would not respond to commands as "Molly".
Molly appears rather stubborn at her introduction, barking at Dave constantly and demanding he help her continue the search for her previous owner, Big Jim Sullivan. She growls often and appears unbothered by the horrors that Dave and John witness daily, even taking down the "baddies" herself at times. Dave uses Molly as "monster bait" frequently by sending her before him into haunted rooms or houses. Without Soy Sauce in her system, Molly retreats to her normal "happy dog" mindset and seems to only take interest in Dave when he is feeding her.
Molly is an ironic character, as she exists to be John and Dave's guide, yet she is almost completely useless. She interrupts important situations to chase after animals, has a habit of accidentally causing Dave physical pain when he is already injured, and likes biting groins for no apparent reason. Still, Molly is a very loving dog and quickly devotes her life to protecting John, Dave, and Amy.
Molly began as Amy's dog. She ran away one day as she followed Jim to the party where he met John, Dave, and Robert. While there, she bit Robert and inadvertently ingested a small amount of Soy Sauce. With the drug in her system, she gained an unnatural intelligence and psychic abilities. She used her newfound abilities to help John and Dave on their quest to defeat Korrok. She followed Dave home and lived with him for a long period of time. For a short while, she ran away from Dave and befriended a woman called Krissy.
While living with Krissy, Molly was kidnapped by Korrok's slaves and replaced by an exact clone of herself. The Molly clone was dangerous and killed a man while making unnatural noises and floating in the air. When John and Dave were called on the case of the supernatural murderous dog, they accidentally killed the clone. She exploded and the real Molly was reintroduced soon after. After the incident, she returned to living with Dave.
Molly considers herself to be Dave's owner, calling him "her male human". She also gave him the name "Meatsmell" and always refers to him as such. Molly believes she takes care of Dave and protects him from an array of dangers, including himself. When the parasitic alien spiders invaded, Molly became afraid and ran away for a short period of time. She followed Dave's scent and found the contamination facility he was being held in. She also found the secret passageway in and out of the facility, allowing John, Dave, Amy, and Anna to come in and out of the ward.
Molly's supernatural abilities allowed her to sense that Amy was in trouble and came to the rescue when she was about to be killed in TBIFOS. John, while on the Soy Sauce, had frozen time right as a bullet was about to hit Amy. Dave was going to take the bullet for her, but right as John unfroze time, Molly jumped in front of it and saved them both. Molly was buried in Dave's backyard and a small funeral for her was held. John had the honor of eulogizing her.
Molly gained several abilities from ingesting the Soy Sauce. She has supernatural intelligence and is able to understand complex emotions and situations. She can form psychic connections with other people while on the Soy Sauce and was used by John to communicate with Dave in JDatE. Molly's biggest achievement is most likely her ability to drive a car, as she saved Dave from a burning building by crashing his truck through the wall and allowing him a way to escape. Although she cannot speak, Molly has communicated with Dave by leading him in the direction of places he needs to go. Molly is able to sense when Dave, Amy, and John are in danger and can track them down from almost anywhere. Molly can see things that most people and animals cannot, and was able to see and attack the parasitic alien spider that bit Dave in his house. Molly was also able to bypass the time stop caused by John ingesting Soy Sauce after the aerial bombing of Undisclosed.