Definitely not. Justice League is a property of DC Comics. DC and Marvel are two separate comic book universes with their own distinct characters and storylines.
One possible plot could be that the Omnitrix gets malfunctioned and starts sending out energy signals that attract the attention of the Justice League. Ben, in his various alien forms, has to work with the League to figure out what's wrong with the Omnitrix and stop an evil force that is also drawn to the energy. For example, Vilgax could team up with some of the League's villains like Lex Luthor to take advantage of the situation.
One idea could be X23 joining the Justice League on a mission to stop a powerful mutant - hating villain. Her unique combat skills and mutant abilities would add an interesting dynamic to the team.
There are likely some fanfictions of this sort. Fanfiction communities are vast and diverse, and often explore different character relationships. For 'Justice League Action Trickster x Yaoi' fanfiction, you could try searching on platforms that are known for hosting a large number of fan - made stories. Additionally, reaching out to fellow fans of the series in forums or on social media might lead you to some great recommendations.
One possible plot could be that the Death Eaters in the Harry Potter world form an alliance with some super - villains from the Justice League universe. Harry and his friends then team up with the Justice League heroes to fight this combined evil. For example, Superman could use his super strength to take on the giants in the wizarding world while Hermione helps Batman with her vast knowledge to figure out the villains' plans.
The Flash might initially be in denial. He's used to Batman always having a plan and his death would be a huge shock. He would then turn his speed into a tool for investigation, trying to find out exactly what happened. Green Lantern could feel a sense of loss but also be spurred into action, using his ring to try and prevent future tragedies like Batman's death. He might create constructs in Batman's memory to inspire the team.
Definitely not. Justice League is a creation of DC Comics. Marvel Comics has its own set of superhero teams and characters that are distinct from those in the Justice League.
Another place to look is FanFiction.net. It has a large collection of fanfictions. However, the quality can vary. When searching for X23 and Justice League fanfics, be sure to read the summaries and reviews to find the good ones.
One common theme could be the exploration of the Trickster's mischievous nature in the context of a relationship with a Yaoi character. Maybe there's a theme of the Trickster causing some chaos in the relationship while also having deep emotional connections.