Well, it could be that one of the FNAF animatronics gets sent to the Loud House world by accident. Let's say Freddy. Freddy then starts to interact with the family. He might mistake the Loud family for the pizzeria staff. Lincoln and his sisters would have to work together to either fix Freddy and send him back or find a way to co - exist with him. The younger siblings like Lily might be curious about Freddy rather than scared at first, which could add a cute element to the otherwise potentially spooky crossover.
One possible plot could be that Casper, the friendly ghost, gets lost in Royal Woods where The Loud House is located. The Loud kids discover him and at first are scared, but then they realize he's friendly. Together, they help Casper find his way back to the Ghost World while having all sorts of wacky adventures in Royal Woods, like trying to hide Casper from their parents and getting into spooky yet funny situations at school.
A cool plot could be that Mr. Krabs discovers a new market in Royal Woods. So he sends Spongebob and Squidward there to set up a Krusty Krab branch. The Loud kids are excited about the new restaurant, but Squidward is miserable as always. Lincoln and Spongebob team up to make the new Krusty Krab a success, facing challenges like dealing with local competition and getting used to the different customers in Royal Woods.
Well, maybe there's a portal that opens up between Royal Woods and Bikini Bottom. Spongebob and Patrick come through to the Loud House world. Patrick could be really confused by all the human stuff and keep getting into funny situations like trying to eat the furniture thinking it's food. Meanwhile, Spongebob and Lincoln team up to solve a mystery that involves a missing item from both their worlds. It could be something like a special kind of jellyfish that has magical powers and it has ended up in Royal Woods.
One idea could be that the Loud sisters get recruited by WOOHP. Maybe Lincoln accidentally discovers a WOOHP gadget and the spies come to retrieve it. They notice the Loud sisters' unique skills and talents. For example, Lori's bossy nature could be useful for leading missions, and Leni's fashion sense could help with disguises. They all team up to stop a villain who is using a new technology to take over the world.
Well, perhaps the ghouls from Ghoul School are on a field trip to the human world and end up in Royal Woods. They meet the Loud family and chaos ensues at first as the Loud kids are scared. But then they realize the ghouls are friendly. Together, they have to figure out how to get the ghouls back to their school before the sun rises, which is dangerous for the ghouls. And along the way, they learn about each other's cultures and make new friends.
A cool plot for 'the loud house crossover fanfiction' might involve a crossover with 'My Little Pony'. The ponies could come to Royal Woods, and the Loud sisters could be fascinated by their magic and cuteness. Lincoln might have to figure out how to get the ponies back to Equestria while also dealing with his sisters' excitement. Or perhaps the Loud family travels to Equestria and has to adapt to a world ruled by ponies.
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.
Well, it could be about the Loud family getting sucked into the Kingdom Hearts universe. Maybe Lincoln could be the main character who teams up with Sora. They'd go on adventures across different Disney - inspired worlds within the Kingdom Hearts setting, while also trying to find a way back home. Along the way, they might meet some of the Loud sisters who also got trapped and they all use their unique skills to fight off Heartless.
One idea could be that Spongebob and Patrick end up in the Loud House world. They could be really confused by all the human stuff and the big family. Maybe they try to make a Krabby Patty in the Loud House kitchen but use the wrong ingredients and chaos ensues.
One idea could be that the misfortunes from 'No Such Luck' somehow cross over into an alternate universe in the crossover. For example, Lincoln's bad luck could start affecting the other characters from the crossover world in strange ways, like causing their gadgets to malfunction.