I've been thinking about my story line and it will in two different dimension.

First, it will be in shadow puppet animation with 3D character and 2D environment. I will create all my character in 3D and rigging for the animation.The background will have a lot of depth and it will in 2D concept animation.

Example from Harry Potter, The Tale of Three Brother : The character will be in 3D without any colour and will be black and white.

Second, the part when the little girl and her unicorn doll enter into their imagination world. So, I've been thinking to make their changes like from black and white puppet shadow with the help of little magic particle flying in the air.

Here is some example of particle that I will try to create for my scene.

And thanks to Katherine, she show me one of the animation for remembering the Lotte Reiniger cut out animation. It's give me a lot of idea for my own animation project. How they play with the black and white, the light and shadow. The movement of their dancing with the 3D environment until they change into the 2D character with colour.