One idea could be that the Dazzlings try to reform and join the main group of ponies in Ponyville. They struggle to overcome their past of using dark magic to steal harmony and learn to use their powers for good.
Another plot could be that the Dazzlings discover a new threat to Equestria that only they can stop because of their unique magic. At first, the ponies in Equestria don't trust them, but as they start to fight this new evil together, the Dazzlings earn the respect and friendship of the other ponies.
In some fanfictions, Twilight Sparkle and her friends could also be main characters. Since the Dazzlings' actions often intersect with the main group in Equestria. For example, Twilight might try to understand the Dazzlings' motives and find a way to either stop them if they are causing trouble or help them if they are trying to reform. The other ponies like Rainbow Dash, Pinkie Pie, etc., would also be involved in different ways depending on the plot. They might be the ones who first notice the Dazzlings' presence and the strange effects their music has on the ponies in Ponyville.
Well, a plot could involve a villain trying to steal all the cupcake recipes in Ponyville. The ponies then have to work together to protect their precious recipes. It could also be about a pony who has lost their sense of taste and has to go on a journey to regain it by trying different cupcakes. Or perhaps there's a mystery surrounding an ancient cupcake recipe that holds a great secret.
Perhaps a story where Scootaloo and Rumble get into an argument over which pony tribe is better, the pegasi or the earth ponies. But then they are forced to work together when a strange magic starts affecting the ponies of their respective tribes. As they work together, they realize that each tribe has its own strengths and that they were wrong to argue in the first place.
One idea could be that Twilight Sparkle accidentally activates a time - travel spell and ends up in the past, right when Equestria was first being founded. She has to figure out how to get back while also making sure she doesn't change history too much.
One idea could be a time - travel plot where the Equestria Girls go back in time to the founding of Canterlot High. They could witness the first magic being used there and have to ensure that history isn't changed too much. Another idea is a crossover with another magical school from a different franchise. For example, they meet students from Hogwarts and have to learn from each other's magic systems. And a third idea could be a story where they lose their magic and have to go on a quest to find a way to get it back, encountering many challenges and new friends along the way.
One idea could be that some ponies accidentally discover laughing gas in an old, forgotten part of Equestria. They start to giggle uncontrollably and it spreads among the ponies in a comical way, leading to all sorts of silly situations like ponies floating in the air because they're laughing so hard while trying to do normal tasks.
One idea could be a female OC who is a talented artist in Equestria but is too shy to show her work. She then meets one of the main ponies like Twilight Sparkle who encourages her to share her art with the world. Another could be a female OC from a different land who comes to Equestria to learn about friendship and has to overcome cultural differences.
How about a story where a pony princess has a vision of the pirate world in trouble. She sends a group of ponies as ambassadors. These ponies meet the pirates and they soon find out that a powerful sea monster is terrorizing the pirates. The ponies use their magic to try and defeat the monster. In the process, they form unexpected friendships with the pirates. There could be some really fun scenes of ponies trying to navigate a pirate ship and the pirates being in awe of the ponies' magic.
One idea could be that the ponies discover Pokemon eggs in Equestria. They start to raise the Pokemon and learn about their powers. For example, Twilight Sparkle could study the different types of Pokemon moves using her magic knowledge.
One plot idea could be Discord creates a bit of chaos in Ponyville that only Fluttershy can calm. For example, he might make all the animals speak backwards. Fluttershy, with her gentle nature and special bond with Discord, has to figure out how to reverse it. Another could be Discord accidentally transports Fluttershy to a strange magical realm, and they have to work together to find their way back home. They face various challenges along the way that test their friendship.