She is the reader's pet dog. One story details Fifi biting the packet of red goo inside the Vampire in a Can costume, which transforms her into a ferocious vampire poodle.
One bad ending has Fifi trying to save the reader from the vampire animals from the pet shop, but they overtake the reader and drain all of your blood.
Fifi appears in the film Goosebumps. She attacks Lorraine Conyers on her doorstep. Lorraine manages to get away from her. She also appears later in the film when the monsters were going to get Zach, Hannah and Champ on top of the Ferris wheel at the abandoned amusement park where she was shown floating near the Body Squeezers.
Fifi also appears in Goosebumps: The Game, being walked by Mrs. Forster from "Home Sweet Home". In Goosebumps Night of Scares, she appears in Chapter 4, making the werewolf come out by barking. She also appears in Goosebumps HorrorTown as a monster.
In the book, Fifi is described as a big black poodle who grows long fangs after drinking the blood in the packet.
In the film Goosebumps, Fifi is somewhat smaller in size, has white fur, and wears a pink collar around her neck and a pink flower on her head. When she transforms into a vampire, her eyes become red and sharp fangs appear on her mouth.
- In concept art for the Goosebumps film, Fifi has mismatched eyes with one being blue and the other being red. She also has blood around her eyes and wore a pink bow instead of a flower.