Granny

Granny, also known as Alien Grandma, is the main antagonist of the sixteenth book of the Give Yourself Goosebumps series, Secret Agent Grandma.

Secret Agent Grandma
Your grandmother is going to be looking after you since your parents are going away. You have not seen her since you were a small child, but you are told she'll be wearing a purple and yellow outfit. You arrive at the train station, awaiting your grandmother on the platform - but just as you head towards her, another old woman identical to the one on the platform. If you go on the one on the platform and go home, she will reveal herself as this hideous alien imposter as it has a plan to take over the world and you got to come up with a plan to stop her and find your real grandma. One bad ending has her zapping you with a mind-control ray only for you to show her where your mother's rose garden is. She then unearths some alien eggs, to which they all hatch, and she prepares to go conquer the world as you are presumably devoured by the newborn aliens.

Goosebumps HorrorTown
Granny reappears in Goosebumps HorrorTown where she pretends to be Dustin's grandmother and from Ukraine, she arrives in HorrorTown with Dustin, Eric, and Lucy there to greet her. Granny plans to invade HorrorTown before Mr Fleshman can. When Dustin notices bright lights from the sky, Granny decides to sleep in the attic.

Granny would later plant some eggs behind a bush, but would be noticed by Lucy, Dustin would confront her to see what see was doing, and granny would lie to him by revealing that she actually is a government agent, which they would fall for. When Dustin asks what to do in order to help Granny, Granny would make them do several things and after, Lucy asks if Mr Fleshman (whom they previously encountered) was also a government agent, and Granny would say that he was a double agent who was also planning to invade HorrorTown, Granny would make the kids use cookie dough in order to fight the aliens, and ahen they arrived to the crashite of the aliens, Granny would encounter Mr Fleshman and they would both reveal their alien forms.

They would have a fight and Lucy & Dustin would try to get them, when they defeated Mr Fleshman, Dustin would discover that Granny was the new alien queen and would command the body squeezers to destroy them, but she would be defeated by her own cookie dough whenever Eric had some left, Granny had proclaimed to Dustin that she would return in a disguise that he would never discover and then she was be beamed up.

Physical appearance
When assuming her human disguise, Granny takes on the appearance as your grandmother. She has can be seen wearing a distinctive purple and yellow outfit. She has small glasses and grey/white hair. But her real form reveals her as a green alien with three red eyes. In HorrorTown, her design consists of having on a red jacket, blue dress and an red Victorian bonnet. In some early concept art for her design in HorrorTown, she is shown to have almost the exact same look as her look on the book's cover.

Trivia

 * The bad ending where Granny has the reader hypnotized and hatches a bunch of newborn aliens that devour the reader is a likely inspiration for the infant Body Squeezers that appears during the Goosebumps HorrorTown questline, Squeezer Revolution.