A powerful dark entity or an ancient evil awakened in the wizarding world could also be the antagonist. This entity might sense Snape's importance in the fight against the dark side and target him. It could use dark magic to incapacitate Snape, and Moody, being one of the few who can sense the danger, comes to his rescue. The entity could be something that even Voldemort was afraid of or something that has been long forgotten but now resurfaces to cause chaos.
One possible plotline could be that Moody discovers Snape is in a dangerous situation due to some dark wizard's plot against him. Maybe Snape is being framed for a crime he didn't commit, and Moody, with his Auror skills and knowledge, believes in Snape's innocence. He then uses his resources and magic to rescue Snape from an ambush or a false arrest. Another plotline could involve Snape being held captive by Death Eaters, and Moody, despite their past differences, decides to rescue him because he realizes Snape is a crucial part of the fight against Voldemort.
It could be Voldemort. Since Snape is always in a complex relationship with Voldemort in the Harry Potter universe, even in a fanfiction with Rumplestiltskin and the mirror. Voldemort might see Snape's new connection with Rumplestiltskin's magic as a threat and try to stop him.
James Potter is an obvious choice. His constant bullying of Snape made him a sort of antagonist in Snape's school years. His actions towards Snape were cruel and had a big impact on Snape's character development.
Luna Lovegood could be an interesting choice. Her unique and somewhat eccentric personality could complement Snape's brooding nature. She might see through his tough exterior and find the good in him, and their relationship could be based on mutual understanding of the 'outsider' status they both have in different ways.
Luna Lovegood could be an interesting love interest. She has an open - minded and eccentric nature. Her ability to see the good in people, even those like Snape who seem cold on the surface, could draw them together. She might be able to make Snape appreciate the beauty in the world in a way he never has before.
The other Death Eaters could be antagonists. They might not trust Snape completely and try to undermine him. For example, Bellatrix Lestrange could suspect Snape's loyalty to Voldemort and try to expose him while he's alone, which would put him in a very dangerous situation.
The love of Severus Snape's life was Lily Evans. He had deep, unwavering love for her since their childhood. His love for her was so strong that it influenced many of his actions throughout his life, even his decisions in the wizarding war.
Well, in some fanfiction scenarios, Snape might rescue Harry from Azkaban because he discovers new evidence that clears Harry's name. Maybe he uncovers a dark plot by some other powerful wizard who framed Harry, and his sense of justice, despite his past animosity towards Harry, drives him to act.
Well, Harry Potter would likely still be a main character. His relationship with Snape could be even more complex in this fanfiction. Since Snape is a demigod, Harry might be both in awe and a bit scared of him at times.
One common theme is mistrust. Given their personalities in the original Harry Potter series, it's natural for fanfiction to explore how they initially don't trust each other. For example, Snape's double - agent status and Moody's cautious nature can lead to a lot of suspicion between them.