Well, perhaps a mad scientist creates a portal that connects the two universes of The Loud House and Totally Spies. The Totally Spies are lured into the portal and end up in Royal Woods. They meet the Loud family and soon realize that the same scientist is planning to use a powerful device in Royal Woods to control the minds of people all over the world. The Loud kids and the spies then form an alliance. The spies teach the Loud kids some basic self - defense and spy techniques, while the Loud kids show the spies how to blend in with the local community and use everyday objects as tools to stop the scientist.
Obviously, the main characters from The Loud House like Lincoln, who could be the one to bridge the two worlds together. And from Totally Spies, Sam, Clover, and Alex. They would be the main characters as they are the core of the Totally Spies team. Maybe Lincoln's sisters like Luna and Luan could also play important roles, like helping the spies with their local knowledge or unique skills. For example, Luna could use her music to communicate secret messages or Luan could use her pranks to create distractions during a mission.
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.
I think Lincoln from The Loud House and Sam from Totally Spies could team up. Lincoln is smart and good at coming up with plans, and Sam is the most level - headed of the spy girls. They could work well together. Also, Lola and Clover might team up. Lola is all about beauty and winning, and Clover is stylish and confident. They could use their charm to distract villains while the others do the more action - packed parts of the mission.
One idea could be that the Totally Spies are sent on a mission to investigate some strange paranormal activities. They then discover Danny Phantom's world and team up with him to stop an evil force that is using both magic and technology to take over the world. Danny could teach them about the Ghost Zone and they could share their spy skills with Danny.
In this fanfic, the setting could be a mysterious island. The Totally Spies are sent to investigate some strange energy readings. Meanwhile, Martin Mystery and his team are there looking into rumors of a cursed treasure. When they meet, there's some initial tension. However, as they start exploring the island further, they find that the strange energy is related to the cursed treasure. The Totally Spies' ability to hack into security systems and their combat training comes in handy, while Martin Mystery's ability to decipher ancient inscriptions and deal with the supernatural helps them understand the true nature of the curse. Together, they face off against a group of pirates who also want the treasure and the evil spirit that guards it.
One possible plot is that a mad scientist creates a device that can manipulate time. This device falls into the wrong hands and starts causing chaos in both Gotham and the places where the Totally Spies operate. Batman and the spies get caught in the time - warped events. They have to figure out how to reverse the effects while also dealing with the changes in the timeline that are making their enemies stronger. The fanfic could explore how they adapt to these changes and use their unique abilities to save the day.
One idea for a Spiderman and Totally Spies crossover fanfic could be that the Totally Spies are on a mission in New York. They accidentally stumble upon one of Spiderman's battles with a villain. Spiderman is initially suspicious of them but soon realizes they have the same goal of protecting the city. They then team up, with the Totally Spies using their high - tech gadgets and Spiderman his superpowers to take down the bad guys.
A possible plot could be that there is a threat to the world that involves both superpowers and high - tech espionage. The Totally Spies are called in to investigate the technological aspect, while Spiderman is already on the scene dealing with the super - powered part of the threat. They cross paths and at first are not sure if they can trust each other. But as the situation worsens, they realize they need to work together. They combine their unique skills, like Spiderman's web - slinging and the Totally Spies' ability to blend in and use advanced gadgets. In the end, they defeat the common enemy.
It could be the Joker. Imagine the Joker getting involved in a global scheme and teaming up with some international bad guys. His chaotic nature would be a huge challenge for both Batman and the Totally Spies. He would use his usual tricks like laughing gas and mind games, but on a much larger scale.