It could be a female version of Jafar. She could be a powerful sorceress who wants to take over the kingdom ruled by Queen Jasmine. She sees the genderbent Aladdin as a threat to her plans.
Perhaps a group of male chauvinist nobles. In this genderbend world, if the power structure has changed to be more female - led, these nobles might try to undermine the rule of Queen Jasmine and the success of the female Aladdin. They could use underhanded tactics to regain control.
The Sultan himself could capture Aladdin if he were misled into believing that Aladdin was a threat to Agrabah. Maybe some false rumors were spread about Aladdin planning to overthrow the Sultan. So, the Sultan, out of fear for his kingdom and his daughter, orders Aladdin's capture.
One idea could be that the genderbent Aladdin is a street - smart girl trying to steal to survive in the city. She meets a genderbent Jasmine who is a prince disguised as a commoner to explore the city. They team up to outwit the evil sorcerer.
Perhaps a group of anti - technology extremists could be the main antagonists in an Ultron fanfic. They see Ultron as the symbol of all that is wrong with technology and are determined to take him down, no matter the cost. They might use their own advanced, but more rudimentary, technology to fight against Ultron. This would create an interesting contrast between Ultron's high - tech abilities and their more basic, yet effective, methods.
Obviously, Aladdin would be a main character. He could be a young man trying to find his place in the modern world. Then there's Jasmine. She might be a career - oriented woman, perhaps a businesswoman or a scientist. The genie would also be a key character. He could be a magical being trying to adapt to the modern world's rules. There could also be Jafar, who might be a corrupt politician or a powerful businessman out to stop Aladdin and Jasmine from achieving their goals.
A new character could be created as the antagonist. For example, an Uchiha who has been corrupted by the power of the Sharingan and wants to use Naruto's special Uchiha - related abilities for his own evil purposes. This character could be jealous of Naruto's unique position within the Uchiha - related story and try to take it from him.
It could be a rogue ninja who has mastered parkour to an extreme level. He uses his skills to steal important ninja artifacts and Naruto has to stop him. This antagonist would be very fast and agile, making it difficult for Naruto to catch him using normal ninja techniques.
Frieza could be a great antagonist. He has a history with Broly and would be interested in Bulma's technology. He might see Broly's new alliance with Bulma as a threat and try to break it up. Frieza could also want to use Bulma to create powerful weapons or devices for his own evil purposes.
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.
Maybe the main antagonist is an evil organization that has been secretly infiltrating the village. They target Sakura because of her skills and knowledge. They deceive her into believing that her village is the real enemy, causing her to betray her comrades.
A powerful and corrupt intergalactic corporation could be the main antagonist. They want to capture Astro and use their powers for their own profit - making schemes. They have advanced technology and a network of spies and mercenaries to carry out their evil plans.