A possible plot for an MLP Battle Force 5 fanfic is a race against time. Let's say there's a powerful and ancient evil that is about to be awakened in the MLP world. However, only the technology and skills of the Battle Force 5 can help stop it. But the Battle Force 5 doesn't know much about the MLP world's magic, so they need the help of the ponies. The ponies, on the other hand, are a bit skeptical about these strange new allies. So, they first have to build trust while also trying to figure out how to combine their different powers and knowledge to stop the awakening of the evil. This could involve some really exciting chase scenes, battles, and moments of discovery as they explore each other's worlds.
Well, a cool plot for an MLP Battle Force 5 fanfic could be that there's a strange energy wave that disrupts both the MLP world and the Battle Force 5 world. The ponies and the Battle Force 5 members start having strange abilities or problems because of it. They then have to figure out the source of this energy wave, which leads them on an adventure across both worlds. Along the way, they learn about each other's cultures and strengths, and in the end, they manage to stop the energy wave and become friends. It could also involve some of the ponies learning to drive the Battle Force 5 vehicles in a really funny way.
One idea could be exploring an alternate universe where the Battle Force 5 team has different powers or vehicles. For example, instead of their regular rides, they could have flying saucers with unique offensive capabilities.
Another interesting plot could be a tournament where teams from both RWBY and Battle Force 5 compete. But as the tournament progresses, they start to realize that there is a hidden conspiracy behind it, and they must work together to expose the truth and stop those behind it.
One idea could be a story where the heroes from different Jump universes are forced to team up against a new, unseen threat that can manipulate the very fabric of their worlds. For example, a villain who can erase characters' powers or change their personalities.
One idea could be a Beezen character in the MLP world having to adapt to the magic there. Maybe they start off as an outsider and gradually learn to use the magic for good, like helping ponies build better hives or something.
One idea could be a wedding between two ponies from different tribes, like a Pegasus and an Earth pony. They would have to overcome the differences in their cultures and traditions. For example, the Pegasus might have a flying ceremony while the Earth pony has a more grounded celebration. Another plot could involve a wedding planner pony trying to create the perfect wedding but facing all sorts of comical disasters along the way, like the flowers not arriving or the cake getting ruined.
I think Rainbow Dash from MLP would be really interesting. She's bold and loves adventure, so she would probably be very eager to get involved with the Battle Force 5's missions. She could bring her flying skills and speed to the team, and her competitive nature might add some interesting dynamics. Maybe she'd have a friendly rivalry with one of the Battle Force 5 members over who can complete a task faster.
A third idea is a time - travel crossover. The Glitter Force could be sent back in time to when their predecessors first fought against an ancient evil. There, they must learn from the past and use the knowledge to prevent a recurrence of the same threat in their own time. They could also form unexpected alliances with the earlier Glitter Force members and discover new aspects of their own powers along the way.
A simple yet interesting plot could be that Spike eats something he shouldn't have and gets sick. For example, he might have eaten a magical plant that gives dragons a stomachache. His friends then have to figure out how to make him better. Rainbow Dash could fly around to find an antidote, while Rarity could sew him a warm blanket to keep him comfortable.
One idea could be an alternate universe where the ponies have different elemental powers. For example, instead of Twilight Sparkle being a unicorn with magic related to friendship, she could control time. This would change the entire dynamic of the stories and the relationships between the ponies.
One idea could be that all the ponies from different tribes come together to face a final, great evil that threatens Equestria. They combine their unique magic and skills to defeat it and in the process, they create a new era of harmony where all differences are truly celebrated.