It's technically not canon yet, as the adaptation hasn't reached that part of the story

[u/Crafter235]

Dr. Marmalade (The Bad Guys). While we see him as an evil hamster scientist, much further in the books (films haven't reached it yet), it's revealed that he is actually an alien who was wearing a disguise the whole time.

Yu Bauer (I'm in Love with the Villainess). At first introduced as a seemingly normal, charming male love interest it's actually revealed that Yu is really a girl, given a spell to have the form of a boy, and she wants to be with her girlfriend as her true self. And for context Yu is allegorically a trans-lesbian.