In some fanfictions, Snape gets revenge on the Death Eaters who wronged him. He could expose their secrets or undermine their plans in a very clever way. For example, he might plant false information among them that leads to their own downfall. Snape's knowledge of the Dark Arts and his intelligence would be key in this kind of revenge plot. He could also use his connections within Hogwarts to set up situations where the Death Eaters are caught off - guard.
Another plotline could be Snape getting revenge on the Order of the Phoenix members who doubted him. He might prove his worth in a very dramatic way, like saving them from a great danger that he secretly knew about all along but didn't share because of their lack of trust in him.
One possible plotline could be Snape getting revenge on those who bullied him during his school days. He might use his potions skills to create some harmless but embarrassing concoctions for them.
One interesting plotline could be Percy seeking revenge on a new enemy who has wronged his friends at Camp Half - Blood. Maybe this enemy has been stealing magical artifacts from the camp, and Percy decides to use his water powers and his wits to track them down and make them pay.
Some fanfictions might have Harry getting revenge on the Ministry of Magic for their incompetence and corruption. He could expose their wrongdoings to the wizarding public and bring about a new era of transparency and fairness in the magical government.
A great plotline is when fanfiction delves into how Snape's relationship with Lily affects his interactions with the Marauders. Since he loves Lily and she is friends with the Marauders, it creates a complex dynamic. In some fics, Snape might try to protect Lily from the potential harm that could come from the Marauders' more dangerous pranks.
A common plotline is an alternate universe where Snape is not as bitter and Hermione befriends him more easily. They could be involved in a battle against a new dark force, and their combined intelligence and magic powers are crucial for victory. Also, there could be a plot where Hermione accidentally enters Snape's mind through some experimental magic and discovers his deepest secrets, which then changes their relationship.
One interesting plotline could be Daenerys seeking revenge on those who betrayed her in the original series. She might use her dragons to lay waste to their cities and armies.
One interesting plotline could be Snape's internal struggle as he tries to save the Potters. He has complex feelings towards James Potter, yet his love for Lily drives him to protect the family. Maybe he has to outwit Voldemort's inner circle without revealing his true intentions.
In some 'Snape Adopts Harry' fanfictions, there is a plotline where Snape and Harry have to work together to uncover a mystery at Hogwarts. This mystery could be related to the Dark Arts or some hidden secrets of the school. Along the way, their relationship evolves from a reluctant guardian - ward relationship to a more loving father - son bond. Harry might start to understand Snape's past actions and Snape, in turn, learns to open up and be more affectionate towards Harry.
Perhaps a plot where Severus discovers his demigod heritage and has to balance it with his life at Hogwarts. He could struggle with how to use his new - found powers without drawing too much attention, while also dealing with his complex relationships with other characters like Harry Potter.
One interesting plotline could be Snape realizing that Harry is not like the 'Boy Who Lived' (WBWL) as everyone expected. Maybe Harry has a different approach to magic that Snape initially scoffs at but later comes to respect. For example, Harry might be more interested in the darker arts in a way that challenges Snape's views.
Well, sometimes in these fanfictions, a great plotline is Snape trying to protect Luna from the bullies at Hogwarts. Given Snape's own experiences of being bullied as a child, he would be very determined to make sure Luna doesn't go through the same. He might use his position as a teacher to subtly intimidate the students who pick on her. Also, there could be a plot where Luna starts to teach Snape about the beauty of the natural magic around them. Snape is so focused on the academic and often darker aspects of magic, that Luna's view of the magic in simple things like a butterfly's flight or the way a flower blooms could be eye - opening for him.