The Queen of Hearts is a likely candidate for the main antagonist. Since she is already known for her tyrannical rule in Wonderland, she might see Alice's shrinking as an opportunity to play some cruel games with her. She could set up impossible tasks for Alice to complete in her shrunken state, with the threat of 'off with her head' if she fails.
The Caterpillar could be the main antagonist. He has always been a bit of an enigma in Wonderland. Maybe as Alice shrinks, he sees her as a threat to his control over the small part of Wonderland he rules and tries to stop her from exploring further.
Well, perhaps the shrinking is a result of some magic gone wrong. As she shrinks, she loses her confidence at first. But then, she realizes that her new small size gives her an advantage to explore hidden corners of Wonderland. She could find secret passages or solve mysteries that were impossible for her at her normal size.
Definitely Alice, as she is at the core of any 'Alice in Wonderland' - based story. The Caterpillar could be another important character in this kind of fanfic. The Caterpillar, which is already a symbol of transformation in the original story, could have a more complex role as it observes Alice's slow shrinking. Maybe it could offer some sort of guidance or be a source of knowledge for Alice as she deals with her changing size in this new version of the story.
Well, there could be a little mouse. Since Alice is shrunk, the mouse could be her guide in this new, small world. It might show her where to find food or shelter.
The Queen of Hearts could be the main antagonist. She is known for her tyrannical rule in Wonderland. Her desire for absolute control could put her at odds with Batman, who is used to fighting against those who abuse power in Gotham. She might see Batman as a threat to her reign and try to eliminate him.
Well, in this type of fanfic, the slow shrinks can enhance the exploration of the strange and illogical world of Wonderland. As Alice shrinks slowly, she may have more time to interact with the various characters she encounters. For example, her conversations with the Cheshire Cat or the Mad Hatter could be more in - depth and revealing, as she is changing size gradually and they might react differently to her continuous shrinking.
Another option could be a corrupted version of Asriel. Maybe Alice's arrival somehow stirs up the darker parts of his past and he becomes a force against her, believing she is a threat to the delicate balance in the Underground.
It could be an unknown force that manipulates the events around Naruto to drive him insane. This force could be an ancient evil that has a vendetta against the Uzumaki clan. It secretly plants seeds of doubt and chaos in Naruto's life, causing him to question everything he knows and trusts, slowly pushing him over the edge.
The White Rabbit could be her mentor. Since he is always in a hurry and seems to know a lot about the workings of Wonderland, he could guide Alice in understanding time management in this strange world, which is a form of growth.
In the fanfic, the act of Alice eating the apple and shrinking could lead to a self - discovery journey. As she gets smaller, she realizes things she never noticed before. She might also develop new relationships with the small beings she meets. The story could explore themes like the perception of size, and how changing one's physical state can also change one's perspective.
It could be a new vampire who is jealous of Bella's relationship with the Cullens. This vampire might have some special power that allows them to manipulate memories, like Alice's memories of Bella. They see Bella as a threat to their own plans in the vampire world, so they try to create chaos by making Alice forget about her.