Countess Yvonne appears in the book. She is featured in some bad endings.
- The reader throws a glass of blood in Countess Yvonne's face and she is swarmed by the other vampires trying to lick the blood off her. Instead of escaping, the reader join the other vampires and try to drink some of the blood. The reader gets scolded for making that decision and are advised to close the book and repeat "It is not normal to drink blood." The book tells you how weird the Reader is and speculates that the Reader may be a real vampire.
- Countess Yvonne and the other vampires have drained Gabe of his blood and she locks the Reader inside one of the coffins for years to come....until she decides to free the Reader.
She also makes a cameo appearance in the Goosebumps movie portrayed by Maryann Gorka, but was credited as "Monster #10." She appears as part of Slappy's army of monsters when released alongside the other monsters. She can be seen during the scene when the monsters chased everyone in the Gym.
- Even though Yvonne and Fifi the Vampire Poodle are from the same book, Yvonne isn't seen until the bonfire scene. However, she had to have been roaming around since Fifi is see attack Lorraine Conyers. It could be possible that Yvonne left Fifi in Lorraine's door and/or that Please Don't Feed the Vampire! was the first book Slappy was seen opening after releasing the Lawn Gnomes and Haunted Car.
- The ending in which the vampires drain Yvonne's blood is similar to Vampire Queen Akasha's death in the book The Queen of the Damned by Anne Rice.
- In Goosebumps HorrorTown, she is Count Nightwing's wife.