This is my first theory. They were the best of friends and they did everyting together. Slappy and the other monsters had defended Stine from the bullies that picked on him at school. I kinda have a feeling that Slappy had snuck to school with Stine just because he wanted his Papa to feel safe. But here is the catch, Slappy was disguised as a student by wearing a black hoodie and a beanie and just hid near the lockers just to keep an eye on Stine and he wouldn't get recognized. He also had an alliases which was "Slade" because he didn't want those kids to make fun of his real name. I also think that Stine and Slappy had always walked home from school together and play fighted all the way back. But, Stine had to hide Slappy away from his parents because they didn't know aobut Stine had a magical typewriter. Slappy was also allowed to hang out with Stine and his friends, and yes Aunt Lorraine was one of the kids that had went to school with Stine and was basically the only one who never mdae fun of him. But once Hannah was created, it all went downhill for the two of them because since Stine was older, he had wanted a child of his own who was human and Slappy was starting to get out of hand and was becoming a danger to the town. This now leads to the evnets of the first movie.
The final theory I have is that Stine was in college at the time that Slappy was created. Stine had found the magic typewriter at an old antique store and took it home with him. Not knowing about it's powers, he had already created Slappy. And poof, he came out. But Slappy was only a baby at the time and he needed someone to take care of him. So Stine took him in and taught him everything he needed to know like, tying his shows, getting dressed, etc. But when Slappy was 3 years old, he was starting to feel lonely because he had no other monsters to hang out with. So Stine went over to the typewriter and created a second ventriloquist dummy named Wally. Slappy was crazy about him and promised his father they he would always protect and love him. And with that, Slappy had helped Stine take care of his little brother as much as he could and the two dummies became inseperable. Pretty soon Stine had created all of the Goosebumps creatures. But when Hannah was created, Slappy was so jeolous because he and the others weren't getting anymore attention. And just before Hannah was created, Slappy and Wally had a falling out which would eventually make them eneimes. So once Hannah was out of the room one night, Slappy had tried to kill Stine. But before Slappy could give Stine the final blow, Stine had sucked him back into his manuscript.
So what do you guys think????? Comment down below and tell your theories :) :) :) :) :) - Slappy'sGirlfriend2598