Who could be the main antagonist in the 'bill turns dipper into a girl' fanfiction?

Another aspect could be that Bill's transformation of Dipper into a girl has some unforeseen consequences. It could be that there is a magical imbalance in the Gravity Falls world as a result. Dipper, in his new form, might discover new powers or abilities that he has to learn to control, all while trying to find a way to reverse the transformation and stop Bill's machinations.

Perhaps an ancient evil entity that was once sealed away by Deer Dipper's ancestors. It has now been awakened and sees Deer Dipper and Hunter Bill as threats. It uses dark magic and mind - control to try to turn them against each other so that it can regain its full strength and take over their world.

Perhaps an evil mage who actually intended for the transformation to go wrong on purpose. They might want to use Sans' new female form to cause chaos in the Underground. They could be trying to manipulate Sans into doing bad things or using her to get to other important characters.

It could be a new villain who is specifically targeting Gohan because of his new form. This villain might see Gohan's transformation as a sign of weakness or an opportunity to mess with the Z - fighters. Maybe they want to use Gohan's confusion and the chaos it causes among his friends and family to their advantage.

It could be someone who wants to take advantage of Minato's new female form. Maybe a villain who has a vendetta against Minato in his original form and sees this as an opportunity to further humiliate or harm him.

Another possibility is that a group of Koopa minions could be the main antagonists. They might be under the orders of Bowser, but they have their own little schemes going on. They could target Mario - turned - girl because they think she'll be an easier target in her new form, but they are in for a big surprise when she shows her strength.

The Joker could still be the main antagonist. He might find the idea of Batman being a girl extremely hilarious and try to use it to his advantage. Maybe he would try to play mind games with her, thinking that she would be more vulnerable in her new form.

The main antagonist could be a jealous classmate. This classmate has always been envious of Marco's popularity or abilities. When Marco turns into a girl, this antagonist sees it as an opportunity to make his life miserable. They might spread rumors or try to embarrass Marco in his new form.

Bowser could be the main antagonist. He might see Luigi's transformation as an opportunity to mess with Mario and the Mushroom Kingdom. He could try to use Luigi's new form to his advantage, perhaps by trying to make Luigi a spy or by using his new identity to cause chaos among the kingdom's residents.

Ganon could still be the main antagonist. His motives remain the same - to take over Hyrule. But now he might underestimate Link because she's a girl, which could be his downfall.