One interesting idea could be a crossover between Transformers and the Harry Potter universe. Imagine Optimus Prime leading the Autobots through Hogwarts, facing magical threats alongside the wizards. Another could be a Transformers and Star Wars crossover, with the Autobots and Decepticons getting involved in the Galactic Civil War. Maybe the Transformers' advanced technology could have an impact on the balance of power in the Star Wars galaxy.
One idea could be having the Autobots and Decepticons end up in the Bayverse's version of Chicago during a major crisis. They could team up with the local military forces there to fight a common enemy, like an alien invasion that is different from their own Cybertronian battles. Another idea is to have a human character from the Bayverse accidentally stumble upon a hidden Cybertronian relic that has the power to transform Earth's technology in unexpected ways, leading to a race between the Transformers and various human factions to control it.
One idea could be a crossover with the Autobots from Transformers Prime and the Titans from Attack on Titan. Imagine the Autobots having to fight the Titans in a post - apocalyptic world. Another idea is a crossover with the Power Rangers. The Rangers and the Autobots could team up to fight a common enemy that threatens both their worlds. A third idea might be a crossover with the Teenage Mutant Ninja Turtles. The Turtles could use their ninja skills along with the Autobots' firepower to take on a new threat in New York City.
Well, a cool plot might involve Iron Man being accidentally transported to the Transformers' home planet. There, he has to use his wits and his suit's capabilities to survive. He could end up forming an alliance with some of the Transformers, like Optimus Prime, and they come up with a plan to get him back to Earth while also dealing with a threat to both their worlds. This would involve a lot of cool tech - sharing and strategic planning between the two very different kinds of heroes.
In 'Transformers DC Crossover Fanfic', a common idea is a technology - magic mashup. Since Transformers are all about advanced technology and DC has a lot of magic - based characters like Zatanna. The story could be about how they combine their powers to defeat a new type of enemy that is immune to normal attacks. Also, a rescue mission where the Autobots and DC heroes team up to save hostages in a dangerous location is quite popular. And then there's the idea of a shared enemy that is a hybrid of a Decepticon and a DC villain, like a fusion of Shockwave and Brainiac who plans to conquer both universes.
One idea could be that the dragon's fire power can be used to recharge the Transformers in some way. Another is that the Autobots could learn the concept of flying from the dragons and incorporate it into their own designs. Or perhaps the Decepticons try to capture the dragons to use their power for evil purposes, and the vikings and Autobots have to work together to stop them.
One popular idea is the combination of different generations of Autobots and Decepticons. For example, bringing together the classic G1 Transformers with the more modern ones like those from Transformers Prime. Another idea is a crossover with different universes where the rules of transformation or the source of their power is different. For instance, a crossover between the regular Transformers and the ones from the Beast Wars universe. Also, a story where the Transformers cross over into a human - dominated world in a different way than usual, like they become part of a virtual reality game world that humans created.
One idea could be that Lucifer, with his charm and manipulative skills, gets involved in the power struggles among the Autobots and Decepticons. He might try to use their war for his own amusement or to gain some sort of power. For example, he could offer a deal to Megatron to help him defeat the Autobots in exchange for something valuable in the underworld.
Maybe the Transformers end up in Remnant due to a space - time rift. The Grimm might be attracted to the Energon that the Transformers carry. The RWBY teams would have to team up with the Transformers to fight off both the Grimm and the Decepticons if they also show up. Yang could learn some combat moves from the Autobots, which would add a new dimension to her brawler style.
Well, a cool concept for a Ben 10 Transformers crossover fanfiction could be that the Transformers' AllSpark has a strange effect on the Omnitrix. This makes Ben able to transform into new alien - Transformer hybrids. For instance, Four Arms could become a huge hulking form with robotic arms that can transform into different weapons. Also, the Decepticons might try to steal the Omnitrix to use its power to create more powerful soldiers. Meanwhile, the Autobots would team up with Ben to stop them. Maybe there could be a situation where Ben has to use his alien forms' unique abilities in combination with the Autobots' skills to defeat a powerful Decepticon threat.
One idea could be that Sonic and his friends accidentally stumble into the world of the Transformers. Sonic's speed could be a valuable asset in a battle against the Decepticons. For example, he could quickly deliver important messages or parts between Autobots during a fight. Another idea is that the Chaos Emeralds somehow have an impact on the AllSpark, creating new powers or challenges for both the Sonic characters and the Transformers.