I just thought of a AU for Fairly Oddparents:
What if instead of fairies being born as fairies, they were humans who died, and then, depending on how they acted or how they died, they were given a certain task? But some fairies were most likely born as fairies straight away (Peri, Irep, etc.). Then, either Anti-Fairies were born as soon as their counterparts died, or they were someone who looked like their counterpart and was a bad person.
Godparents: Either had kids themselves, babysitter, teacher, parental figure to a younger sibling or a random kid. Possibly died while protecting a child, old age (?), an illness a kid might have had.
Mother nature: Before she died, she probably loved gardening, loved protecting nature/animals, and loved fruits/vegetables? She could've died from food poisoning, a gardening incident, a animal incident or something else.
Cupid: Loved love, was probably known as someone who helped people with their crushes, loved money (maybe rich??) Loved chocolate (especially chocolate heart filled with nougat), possibly died while helping someone on a love mission?
Jorgen Von Strangle: Was most likely some sort of rule lover, maybe worked in the military?, loved to excersise, he probably made sure everyone was doing what they were supposed to do. I'm still thinking of a way he could've died.
Big Daddy: Was definately in the Mafia as the boss, was scary and feared throughout the land and possibly died from a failed assassination or something else.
Tooth Fairy: Was probably a dentist, maybe a high ranking/boss? Loved teeth, especially childrens ones and always maybe told stories to kids about the Tooth Fairy. Maybe died from something she picked up when looking at a patients mouth?
Dr. Rip Studwell: A doctor/actor/golf person, either died from a disease off a patient, maybe a stage incident?? Still thinking of possible ways. I'm thinking that because most doctors choose to stay at home when they die, he might've too.
Pixies: They were probably buisness men (HP was probably the CEO), and were known for being monotone and expressionless most of the time, might've died from a workplace incident.
Animals (Dogs, cats, fish, ferrets, just any house pets): They could've died in a happy family, or they could've had a neglectful family, died, and been given the job to help GodKids. This is maybe a way for them to finally have the love they so desperately wanted.
Edit: So I thought of one or two.
April Fools: A prankster, loved to prank people especially on April Fool's day. Maybe he was the type of person to pull extreme pranks, so maybe he died because of a prank gone wrong
I'm still thinking about other characters :[ but hopefully I think of better ways of how they were like, what they could've looked like, how their life was etc.