Hannah Stoneman is a teenage female werewolf from Werewolf Skin, one of the books from the Goosebumps series, as well as the two-part episode of the TV series.
Hannah befriended Alex Blackwell after he moved to Wolf Creek, and later in the book and the TV episode, they investigated the werewolf sightings in the small town. The werewolves were thought to be the eccentric Martlings, but it was later revealed that Alex's own aunt and uncle, Marta and Colin, were the werewolves. They were caught by Alex removing the werewolf skins inside an abandoned house, and later on, Hannah helped Alex take possession of the skins and remove the curse from Aunt Marta and Uncle Colin.
Both versions featured a twist ending which revealed that Hannah is a werewolf herself. On TV, Alex learns Hannah's villainous secret when he sees her in her own werewolf skin in one of the photos he took, and afterwards, Hannah appeared to Alex and informed him that she doesn't bite.
The book has a much darker ending, with Alex and Hannah in the empty cabin next door and seeing a third werewolf skin. Shortly afterwards, Hannah turned heel by appearing to Alex in the werewolf skin, which she revealed to be her own. After the revelation, the evil Hannah attacked Alex, with the ending leaving the possibility that she may have killed him or turned him into werewolf, while cementing Hannah's heel turn in the process.