You could start by establishing the setting and the situation. Say you choose a crossover with the Avatar: The Last Airbender world. Begin with Gohan SSJ2 sensing an unusual energy in that world and deciding to investigate. This sets the stage for the story to unfold.
Begin with a character's perspective. If it's a crossover with the Pokemon world, start from the view of a Pokemon trainer who witnesses Gohan SSJ2 arriving. Describe their shock and how Gohan's presence starts to disrupt the normal balance of the Pokemon world. This creates an immediate sense of intrigue and a starting point for the fanfiction.
First, decide on the universe you want to cross Gohan with. Then, think about how Gohan would fit into that world. For example, if it's a modern - day Earth setting, consider how he would hide his powers or use them subtly. Next, come up with a basic plot like Gohan has to stop an evil force in this new world.
First, decide which universe you want to cross Mystic Gohan with. Then, research that universe to understand its rules, characters, and overall vibe. Next, think of a good reason for Gohan to end up in that new universe. It could be a magical accident, a portal opening, or some other device. After that, start planning the main conflict or story arc. For example, if it's a crossover with the Star Wars universe, maybe Gohan has to help the Rebels fight the Empire. Then just start writing, introducing Gohan into the new setting and seeing how he interacts with the new characters.
A really cool concept for an SSJ2 Gohan crossover fanfiction would be to put him in the world of Middle - earth from The Lord of the Rings. Gohan's strength and honor would make him a great ally to the Fellowship. He could use his super speed and strength to fight off orcs and other dark creatures. He might also have some interesting interactions with Gandalf, learning from the wizard's wisdom while also sharing his own knowledge of martial arts and ki manipulation.
One idea could be a crossover with the Naruto universe. Gohan as SSJ2 could end up in the Hidden Leaf Village and interact with the ninjas. Maybe he helps in a battle against a powerful enemy using his Saiyan powers.
Begin by establishing the setting clearly. If it's a Joker crossover with a horror universe, describe how Gotham starts to take on elements of that horror world. Then, introduce the Joker in a way that makes sense in this new context. Maybe he's intrigued by the new horrors or sees an opportunity to create more chaos. You also need to consider the characterizations and how they will interact. The Joker's maniacal nature might clash or blend in unexpected ways with the other characters.
First, decide which universe or character you want to crossover with Morbius. For example, if it's Iron Man, think about how their worlds collide. Maybe Morbius' condition attracts the attention of Stark Industries. Then, create an interesting opening scene. It could be Morbius in a situation that leads him to cross paths with Iron Man, like a strange energy signature that both are investigating.
Begin by choosing the right crossover. Let's say it's Negan and 'Harry Potter'. Think about the rules of the 'Harry Potter' world and how Negan would break or bend them. You can start with Negan somehow getting a letter from Hogwarts (maybe a mistake by the owl post). He shows up at the school, and chaos ensues. Write from his perspective as he encounters magic for the first time. His confusion and his attempt to assert his dominance in this new and strange place would make for an interesting start.
Well, start by creating a scenario that brings the Jashin concept into the other story. For example, if it's a crossover with a game world, think about how Jashin's influence could disrupt the game's balance or create new quests. You could also think about the reactions of the original characters to the Jashin - related elements. Maybe they're horrified, or maybe some are intrigued. Then build your plot around these interactions and reactions.
First, choose the two universes you want to cross over. For example, if it's Miraculous and Naruto. Then, think about how the characters will interact. Maybe Ladybug could learn some ninja skills from Naruto. Start with a simple scenario like an akuma attack in a world where ninjas exist.
First, decide which universe you want to cross Chappie over with. For example, if it's "Terminator", research the lore of that universe. Then, think of a plot hook. Maybe Chappie is mistaken for a Skynet creation in the Terminator world. Next, start writing an introduction that sets up the crossover situation.