Oscar Tamaki is a very young wizard. Being only nine he cannot attend Hogwarts yet, let alone have a wand. Yet he has one and regularly visits Harry, Ron and Hermione in my Fanon. He is extremely gifted in magic having learned quickly while young and still unfocused with his magical abilities. Young wizards and witches are prone to using magic accidentally when under emotional stress, ie anger and fear. For example when Harry was very little at school he would change the teacher’s hair colour regularly and once apparated himself onto the school roof. Oscar however has full control of his emotional magic and makes use of it to prank people such as turning them into clowns because he loves clowns.
Despite being magically gifted and a fast learner he is very childish to the point of babyish behaviour. He still sleeps with a teddy bear and sometimes even keeps Teddy with him during the day at Hogwarts. Which results in Malfoy making fun of him.
He also regularly turns himself into a baby and likes wearing diapers/nappies.
When he is not hanging about at Hogwarts he is hanging out with other magical friends at Vonderland or Springwarts. When he’s not doing that he is being tormented by his teddy bear Teddy who likes to sniff him with his big shiny nose.
He gets into messy situations while going on adventures and fighting magical beasts. He goes on many adventures.