Well, an 'Evil Morty' fanfic in the 'Rick and Morty' universe can be really interesting. Evil Morty is such a complex character. In these fanfics, he could be explored further in terms of his motives. Maybe he's tired of being in Rick's shadow or he has some grand plan to take over the multiverse that wasn't fully shown in the show. Fanfics give the writers the freedom to expand on his backstory and what makes him tick.
One more thing that makes these fanfics unique is the way they can twist the relationships in the show. Evil Morty's presence can change the dynamics between Rick and Morty. For instance, Morty might start to question Rick more if he sees what an Evil version of himself is capable of. And Rick might have to reevaluate his relationship with Morty in light of this new threat. This creates a whole new set of story possibilities that are unique to these fanfics.
By putting them in situations where they have to rely on each other. For example, if they are trapped in a dangerous dimension. This would force them to interact and potentially grow closer.
Evil Morty's origin likely began with his exposure to the many dark and unfair aspects of the multiverse. He was probably fed up with the Ricks' arrogance and control. Maybe he had some unique experiences that made him question his place. He could have started small, observing how things worked and gradually formulating his plans. It's also possible that a particular event, like being mistreated by a Rick, served as the catalyst for his turn to evil.
One idea could be that Morty discovers a way to redeem Evil Morty. He tries to show Evil Morty that there's a better way than his villainous path. Morty could use his own experiences of growth and kindness to reach out to Evil Morty.
One main theme is the clash of personalities. Doofus rick is, well, a doofus, while evil morty is calculating. Their interactions often highlight this contrast. For example, in many fanfics, doofus rick will do something silly that throws off evil morty's carefully laid plans.
Yes, there is a story in 'Star vs the Forces of Evil'. It follows the adventures of Star Butterfly, a magical princess from another dimension. She is sent to Earth to learn how to use her magic better. There, she meets Marco Diaz, and together they face various challenges, including battling the forces of evil that threaten both Earth and Star's home dimension. The story is filled with magic, friendship, and a lot of fun and exciting plot twists.
Because they are easy to understand. We can clearly tell who is good and who is bad, like in 'Snow White' where Snow White is the good one and the Evil Queen is bad. It gives a sense of justice being served at the end.