Perhaps they could form an unlikely friendship. Rumble, being a pegasus colt, and Sweetballe, with her own unique charm, might start off not getting along but then discover they have more in common as they work together to help a group of young ponies learn about flying and friendship. They could then have to defend their newfound friendship from those who don't understand it.
Well, clearly Sweetballe and Rumble are the main characters. Sweetballe might be a pony with a kind heart and some special abilities or qualities. Rumble, as a pegasus, is likely to have flying skills and a personality that can either complement or contrast with Sweetballe's.
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 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.
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.
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.