One idea could be a character from Naruto ending up in the Descendants' world. For example, Naruto himself could be transported there. He might use his ninja skills to deal with the challenges in the Descendants' world, like facing off against the villains in a very different way compared to the Descendants' characters. Maybe he'd use his shadow clone jutsu to confuse the bad guys or his Rasengan to take on powerful foes.
Another plot could involve a Descendants character coming to the Naruto world. Mal could arrive in Konoha. She would find the ninja world full of new and strange powers. Her magic would be a novelty there, but she'd also have to learn to deal with the more combat - oriented nature of the Naruto world. She could form an alliance with some of the ninja clans or perhaps even start a rivalry with some of the more headstrong ninja.
A more complex plot could be that there is a mix - up of magic and chakra. The Descendants' magic starts to seep into the Naruto world and vice versa. This causes chaos as ninja start to develop magical abilities and the Descendants' characters start to gain some ninja - like powers. Naruto and his friends have to work with the Descendants' crew to find a way to reverse this before both worlds are destroyed.
One idea could be a crossover with the 'Dragon Ball' universe. Naruto's descendants could team up with Goku's family to fight a common enemy. Another could be a crossover with 'One Piece', where they sail the Grand Line together in search of a powerful treasure that could change both their worlds. Or perhaps a crossover with 'Bleach', and they battle Hollows and Soul Reapers together in the afterlife.
One idea could be that a character from 'Once Upon a Time' (OUAT) accidentally travels to the world of 'Descendants'. For example, Emma Swan could end up there and have to deal with the different rules and characters. Maybe she tries to help some of the 'villain kids' in 'Descendants' to see that they don't have to follow in their parents' footsteps, just like she often helped people in OUAT find their true selves.
One idea could be that the characters from Descendants end up in the world of Jessie by some magical mishap. Mal could use her magic to help Jessie deal with some of the difficult kids she babysits, like when they get into trouble at school. Another plot could be that the kids from Jessie visit the Isle of the Lost out of curiosity and try to bring some positive change there. Maybe they start a music club or something similar to engage the villain kids in a more positive activity.
One idea could be that the demigods from Percy Jackson's world accidentally end up in the Descendants' universe. They could team up with the VKs (Villain Kids) to face a common threat that is related to both Greek mythology and the magic in the Descendants world. For example, an ancient Greek monster that has been awakened by the dark magic in the Isle of the Lost.
One idea could be a story where the characters from 'Descendants' end up in the 'Twilight' world. For example, Mal could meet Bella and they could form an unlikely friendship. Mal might be intrigued by Bella's relationship with Edward and the whole vampire - human dynamic in the 'Twilight' world.
Maybe there's a plot where a powerful and rare Pokemon is causing chaos in the Naruto world. The Naruto characters have to team up with some expert Pokemon trainers from the Pokemon world to stop it. Naruto could learn about the unique bond between trainers and Pokemon and apply some of those concepts to his relationships with his friends. And the Pokemon trainers could be in awe of the ninja techniques and use some of that knowledge to improve their own strategies.
A possible plot is that the Zoids themselves gain some of the abilities of Naruto characters. Imagine a Zoid being able to use chakra and perform ninjutsu. A Fire - type Zoid could use the Fireball Jutsu. This would completely change the dynamics of Zoids battles. Also, the story could revolve around a group of Naruto characters trying to stop an evil force in the Zoids world that is using Zoids in a way that could destroy both the Zoids world and the Naruto world. They would have to learn about Zoids and team up with local Zoid pilots to fight against this common enemy.
One idea could be that members of Root are sent to infiltrate the Hidden Leaf under the guise of being friendly shinobi. They cross paths with Naruto and his friends. Naruto, being the perceptive one, senses something off about them. This could lead to a series of battles and mind games as Naruto tries to expose their true motives.
Maybe there's a crossover where the Kyuubi's chakra has some strange effect on the Gargoyles. It could either enhance their powers in unexpected ways or cause some sort of chaos that they have to work together to fix. For example, the Kyuubi's chakra might accidentally awaken an ancient evil in the Gargoyles' world, and Naruto and the gargoyles must use their combined strength and wits to stop it.
Maybe in this crossover, Naruto has a vision of the Traveler from Destiny. Curious, he somehow manages to cross over to the Destiny universe. There, he meets the different classes of Guardians. He could learn about their weaponry and powers and in turn, teach them about chakra. They could then work together to stop a Vex invasion that is spreading across both universes.