Marta Blackwell
Marta Blackwell is a villainous female werewolf from Werewolf Skin, the 60th book from the Goosebumps series, as well as the two part episode of the Goosebumps TV series.

Marta Blackwell and her husband, Colin, live in Wolf Creek, where their nephew, Alex, moves to live with them. There were stories of werewolves roaming at night in Wolf Creek, and in Part 1, Alex faced them as they tried to enter through his bedroom window. In Part 2, Marta inserts the idea in Alex's head that the Martlings, their eccentric next door neighbors, are the werewolves, stating that they attacked Hannah Stoneman's brother some time ago.

However, Marta turned heel when she was revealed as a werewolf, along with Colin, and they were caught by Alex going into the abandoned house that they claimed the non-existent Martlings lived, and removed their werewolf skins. Knowing that his aunt and uncle are under the spell of the pelts, Alex and Hannah took the skins and buried them. However, with the full moon closing in, the evil Marta appeared with Colin and begged Alex to give them their pelts, which came to life and attempted to attack Alex. Once the full moon appeared in its entirety, the skins were destroyed, and Marta and Colin were free from their curse.