Well, you could write a 'big baby fanfiction' where the big baby is actually a character from another dimension who gets stuck in a world where everyone is normal - sized. The story could revolve around the big baby trying to find a way back home while causing all sorts of chaos and also learning valuable lessons along the way. For example, they might learn about friendship from the people who initially feared them but then came to understand them.
One idea could be exploring the daily adventures of a big baby in a magical world. Maybe they have special powers despite being in a baby - like state. Another could be about how the big baby forms unique friendships with other characters who are initially puzzled by this big baby concept.
One idea could be Big Chill Baby getting lost in an unknown dimension and having to find its way back home while making new friends along the way. Another could be Big Chill Baby learning a new power that no other of its kind has, which then attracts the attention of both allies and enemies.
A really fun 'baby daisy and baby luigi fanfiction' could be set in a world of toys. They are toys themselves and they have to work together to escape from the clutches of an evil toy collector. They make friends with other toys along the way and use their unique skills, like baby Daisy's ability to find hidden paths and baby Luigi's courage, to overcome the challenges.
One idea could be to explore the Boss Baby's adventures in a different city. Maybe he gets sent on a secret mission to Paris and has to deal with French baby competitors. Another could be a time - travel story where the Boss Baby goes back to the era when his parents were kids and tries to change something in their past that would affect his present situation.
A baby Homura fanfiction could focus on how she copes with the strange world around her. For example, she might be confused by the adults' actions and try to find her own sense of order. Maybe she starts to create her own little 'rules' in the house, like always arranging her toys in a certain pattern, which could be a sign of her future organized self in the original Homura story.
One interesting idea could be the unique way the baby's perception is shown while hypnotized. Maybe the baby has extraordinary dreams or visions that are not possible in a normal state.
Well, you could write a baby robin fanfiction where the baby robin is found by a kind-hearted child. The child tries to take care of the robin, learning about its needs and how to keep it safe. But then they have to face the dilemma of whether to keep the robin or set it free when it grows stronger. It can be a heart - warming story about friendship and responsibility.
One idea could be about baby Spyro's first flight. Maybe he's a bit clumsy at first and keeps crashing into soft bushes, but with the help of his dragon elders, he gradually gets the hang of it. Another could be baby Spyro making his first friends among the other small creatures in his world. He might be a bit shy at first but then discovers how fun it is to play with them.
A baby Alastor fanfiction could explore his relationship with other characters when he was young. For instance, perhaps there was a kind neighbor who noticed his strange behavior but instead of being afraid, tried to help him understand his powers. This neighbor could introduce him to music, which later becomes an important part of his character as Alastor grows up.
One plot idea could be that Baby Loki gets into some sort of magical mischief in Asgard while Thor tries to keep him out of trouble. For example, Loki might accidentally turn all the flowers in the palace gardens into snakes, and Thor has to figure out how to reverse it before the other Asgardians find out.
One idea could be that baby Mario and baby Luigi get lost in a magical forest filled with strange creatures. They have to use their baby wits and little jumps to get through obstacles and find their way back home. Maybe they befriend a little fairy who guides them part of the way.