A common plot twist is that Snape saves James but at a great personal cost. Maybe he has to sacrifice his standing in the wizarding community or make a deal with a dark force. For instance, he might have to give up some of his valuable potions knowledge in exchange for James' life.
It can be considered common in the realm of Harry Potter fanfiction. Snape's love for Lily was so profound that imagining him saving her and James, despite their differences, is a fascinating plot point. Many fans are drawn to exploring the untapped potential of this scenario in their own creative works.
One possible plot twist could be that Hermione discovers a hidden prophecy that only she can fulfill to save Snape. This prophecy might be related to some ancient magic that Snape has unknowingly become a part of. Another twist could be that in order to save Snape, Hermione has to team up with some of her former enemies, like Draco Malfoy, who also has a vested interest in Snape's survival for some reason. And perhaps the most unexpected twist could be that Snape's salvation is somehow linked to Hermione's ability to time - travel, which she uses to go back and change certain events that led to Snape's peril in the first place.
Well, often in these fanfictions, a plot twist is that Snape enters with a secret mission related to Harry. It could be that he has been working undercover for a group that wants to protect Harry from a greater threat than Voldemort. Or, Snape enters and it turns out he has a connection to Harry's magic that was previously unknown. For example, he might be able to unlock a new level of Harry's powers. Also, Snape could enter in a scenario where he and Harry are forced to swap bodies, which leads to all kinds of humorous and also deep - understanding - building situations between them.
A common plot twist could be that Snape is actually Harry's real - life protector all along. He pretends to be mean in public but in private, he is training Harry for some greater purpose. Another could be that Snape's niceness is part of a deal he made with Dumbledore that we don't know about in the original story. Maybe Dumbledore asked Snape to be extra nice to Harry to boost his confidence.
In this type of fanfiction, a plot twist could be that Snape saves them, but they end up having to go into hiding in a completely unexpected place. Maybe they have to live among muggles in a way they never thought possible. Another plot twist could be that Snape saves them, but then realizes that he has put himself in a very dangerous position with Voldemort's followers. So he has to find a way to protect himself while also protecting Lily and James. And there could also be a plot twist where Snape saves them, but they don't believe his motives are pure and they try to escape from him, leading to a whole new set of adventures and challenges.
One common plot twist is when Lily discovers Snape's deeper involvement with the Dark Arts later than expected. This realization makes her lash out at him more harshly than before, causing great pain. For instance, she might find out about some of his secret experiments or associations.
One popular plot twist could be that Snape is actually controlling Hermione to protect her from a greater danger that she's unaware of. Maybe there's a dark wizard targeting her and Snape's control is a way to keep her out of harm's way while he figures out how to defeat the threat.
A really interesting plot twist could be that Snape was under a spell all along that made him seem so cold and distant, and Hermione discovers it. This changes the whole dynamic between them. Another twist could be that Hermione is actually related to someone from Snape's past in a way that they never expected, which brings them closer.
One common plot twist is that Snape was forced to hide his fatherhood due to some dark magic threat. Another could be that Harry's mother had some sort of pre - arranged deal with Snape that led to Harry's birth.
One popular plot twist could be that they return with new magical abilities. Maybe they've gained the power to control time, which would add a whole new layer to the story. They could use this to prevent their own deaths or change other major events in the wizarding world.