The plot could involve a new threat emerging that affects both worlds. This threat could be a powerful sorcerer who wants to combine the technology of the TMNT world with the magic of Ninjago. The Ninja and the Turtles would have to put aside their differences and work together. They would travel between the two worlds, exploring each other's unique environments like the Ninjago Monastery and the TMNT Lair.
A possible plot could be that a group of ninjas from Ninjago's past, who were exiled for misusing their powers, have found a way to cross into the TMNT world. They team up with the Foot Clan to take over both worlds. The Ninja and the Turtles must then join forces. The Turtles' street - smart knowledge and the Ninja's ancient wisdom would be crucial in outwitting their enemies. Along the way, there could be some fun moments like Michelangelo trying to learn how to do Spinjitzu.
One idea could be that the Ninja from Ninjago are transported to the TMNT's world. They team up to fight a common enemy like the Shredder who has somehow got hold of some dark magic from Ninjago. The Ninja can show the Turtles their unique fighting styles and the Turtles can introduce the Ninja to the sewers of New York as a base.
Imagine if there was a tournament that brought the best fighters from both universes together. Naruto, Sasuke, and the others from the Naruto world, and Kai, Jay, and the rest from Ninjago. They start off competing against each other but then realize there is a greater threat lurking. A group of shadowy figures wants to steal the powers of both ninjas and warriors. So, they must put aside their differences and combine their skills to fight this new enemy.
One possible plot could be that the ninjas from Ninjago accidentally stumble into the world of Chima while on a mission through a magical portal. They find that the animal tribes in Chima are facing a new threat that they can't handle on their own. The ninjas decide to help, using their unique skills. For example, Kai could use his fire powers to combat an ice - based enemy that the Chima tribes are struggling with. Meanwhile, the Chima characters could introduce the ninjas to their own ways of fighting, like using their vehicles and the power of Chi. This would lead to an exchange of fighting styles and strategies, and in the end, they would defeat the common enemy together and the ninjas would find their way back home.
One idea could be that the Turtles from 2003 get transported to the 2012 universe and they have to deal with the different versions of their enemies. For example, the Shredder in the 2012 version might have some new powers or tactics that the 2003 Turtles aren't used to.
A possible plot is that an ancient evil that was sealed away in the 2003 universe is accidentally awakened by the arrival of the 2012 turtles. The 2003 turtles initially blame the 2012 ones but then realize they need to work together. They combine their strengths, with the 2012 turtles' modern thinking and the 2003 turtles' deep knowledge of ancient ninja lore, to defeat the evil.
One idea could be that the Turtles from 1987 end up in the 2003 universe and have to adapt to the darker and more serious tone. They could team up with the 2003 Turtles to fight a common enemy like the Shredder. The 1987 Turtles' more light - hearted and comical ways might initially clash with the 2003 Turtles' brooding nature, but they eventually learn from each other.
One possible plot could be that the Teenage Mutant Ninja Turtles somehow end up in the Freddy Fazbear's Pizza place. Maybe they are investigating some strange disappearances that are rumored to be related to the animatronics. They could use their ninja skills to navigate the dark hallways and face off against the haunted animatronics. The turtles' unique personalities would add a fun dynamic, like Mikey being scared at first but then finding the whole situation exciting, while Raph is ready to fight from the start.
A possible plot for this crossover fanfiction is that the worlds of Ninjago and Chima start to merge due to some magical mishap. This causes chaos as the different species and cultures collide. The heroes then have to figure out how to separate the worlds again. For example, the ninja from Ninjago might have to work with the lions from Chima. Another idea is that a group of villains from both worlds team up and the heroes have to form an alliance of their own. They would need to overcome their differences and learn from each other's fighting styles. There could also be a story where a Ninjago character is transported to Chima and discovers a long - lost relative from there, which adds a personal touch to the adventure.
One possible plot could be that the Monkie Kid characters accidentally end up in the Ninjago realm. They meet the Ninja and at first there are misunderstandings as they don't know each other's powers and motives. But then they realize they have a common enemy, like an ancient evil that threatens both their worlds. So they team up, with the Monkie Kid using his magic staff and the Ninja using their elemental powers to fight this great evil.
One idea could be that the Turtles end up in the Underground world of Undertale. They might have to navigate through the various regions, like Snowdin or Hotland, using their ninja skills. For example, they could use their stealth to avoid some of the more dangerous monsters. Another plot could involve the characters from Undertale being brought to the Turtles' New York. They would then have to deal with the Foot Clan and other threats in this new, strange environment.