The plot could involve the child reader being lost in a strange and somewhat scary place. Slappy, who is familiar with this place, decides to help the child find their way back home. Along the way, they have conversations about their different perspectives on life. Slappy teaches the child some of his 'tricks' which are not really harmful but more like fun illusions, and in return, the child shows Slappy the beauty of simple things like the sound of a running stream or the sight of a colorful bird. This forms the basis of their friendship.
One possible plot idea could be that Slappy, despite being a spooky character, and the child reader start off on a wrong foot. Maybe Slappy scares the child at first. But then as time goes on, they find common interests like a love for old books or mystery stories. They start to bond over sharing these interests and eventually become good friends, with Slappy protecting the child from other real threats in the spooky world they inhabit.
In a forest setting, Slappy could use his knowledge of the forest's secrets to show the child reader some hidden paths and beautiful, magical glades. The child could introduce Slappy to the idea of having a picnic and sharing food. This new experience for Slappy would bring them closer as friends. In a school setting, the child might be getting bullied. Slappy could use his spooky appearance to scare off the bullies, and then comfort the child. This would strengthen their bond as the child realizes Slappy is a true friend.
A simple plot could be that the reader is a student at a school where Slappy has been accidentally brought to life. The reader has to figure out how to stop Slappy from causing chaos in the school before it's too late. Maybe they find an old book in the library that has the key to putting Slappy back to sleep.
One idea could be that Slappy somehow enters the real world and tries to befriend a lonely child. He uses his spooky charm to make the kid feel special at first, but then things start to get out of hand as his true mischievous nature emerges.
A local magician could be the main character. He has some knowledge of the supernatural and realizes that Slappy is a dangerous entity. He then tries to use his magic skills to either defeat Slappy or send him back to where he came from.
A great plot for MLP Friendship Games fanfiction could be that there's a malfunction in the portal between Equestria and the human world during the games. As a result, some of the pony versions of the characters start appearing in the human world during the games. This creates chaos as they don't understand the human world rules and the Equestria girls have to quickly teach them while still trying to win the games.
One plot idea could be that Stiles and Jackson get stranded in the woods during a camping trip. They have to rely on each other to survive, building a deeper friendship as they face challenges like finding food and shelter. Another could be that they are paired up for a school project that forces them to spend a lot of time together. At first they clash, but then they start to understand each other better. A third idea is that they both witness a supernatural event that no one else believes. They form a bond over keeping this secret and trying to figure out what's really going on.
One idea could be Sonic and Tails going on a journey to find a rare power - up that could save their world. Along the way, they face many challenges and Sonic always protects Tails, which deepens their friendship. Another plot could be Tails getting lost in a mysterious forest. Sonic searches for him non - stop, and when he finds Tails, Tails realizes how much Sonic truly cares for him.
In a fanfiction, the reader might be a new neighbor in a town full of Goosebumps - like mysteries. Slappy, being the mischievous dummy he is, decides to play tricks on the reader. But as time goes on, the reader outsmarts Slappy's tricks and instead, they form an unlikely friendship. They end up going on adventures together, exploring the spooky parts of the town that others avoid.
One idea could be that the child was the result of a past relationship that Sakura kept hidden due to the dangerous nature of the other person. Maybe the father was a powerful enemy who she had to defeat, and she was afraid of the child being used against her.
One possible plot idea could be that they meet at school for the first time. Maybe Deku is being bullied and Uraraka stands up for him. This would start their friendship early on. They could then discover their shared dreams of becoming heroes together.