The Prodigy (Male AP and AR?)
 

https://www.youtube.com/watch?v=3FPuKRJikWs It seems this upcoming movie will feature a boy who has an adult psycopath alter ego, one shot shows his shade growing in height and well... near the end you can see a glimpse of her grown up form. Idk if this will be a monster or a human like it suggest, but we can hope for some onscreen process.