Cuddles the Hamster

Cuddles is a hamster that ate Monster Blood and grew to about ten feet. His only appearance to date is in Monster Blood II and is technically the main antagonist of the book. Despite his limited appearances, Cuddles is one of the more popular characters in the series.

Monster Blood II
In Monster Blood II, Cuddles is owned by science teacher Mr. Murphy, who punishes Evan Ross to clean Cuddles' cage, whom Evan dislikes. To get back at Mr. Murphy for Evan, Andy feeds Cuddles some Monster Blood. But after a while, he grows to an enormous size and starts rampaging through the school. Evan eats some Monster Blood himself, so that he can grow to Cuddles' size and do battle with him. However, Cuddles is about to finish Evan off, until they both return to their normal sizes. It turns out that the expiration date on the Monster Blood has passed, resulting in the magic wearing off. As a present, Cuddles is given to Evan. In the end, it is heavily implied that Cuddles ate some more Monster Blood from a new can.

Return to HorrorLand
Cuddles is briefly mentioned in Return to HorrorLand. It was when Derek and Margo Strange interview Evan, who retells the events of Monster Blood II.

Goosebumps film
Cuddles appears in the second draft of the Goosebumps film as the "pet" of Slappy the Dummy. He is first seen attacking Clem the Horror after the Monster Police failed to capture R.L. Stine.

Trivia

 * Despite only appearing in one book (not counting the video footage in Return to HorrorLand), Cuddles has grown to be a very popular character in the Goosebumps franchise, given the fact the character has been used a lot in promotional material and merchandising.