Steven Yeunhas been cast in the upcoming theatrical film coming from the world of Avatar: The Last Airbender. The character the Invinciblestar will be voicing remains a mystery, as Paramount wants to keep plenty of surprises for when audiences return to this world in theaters early next year. Just like the characters that will attempt to make the upcoming movie an unforgettable experience, the premise for the project remains under wraps. It will take a while for audiences to discover what Steven Yeun will be up to when he enters the world of Avatar: The Last Airbender.