Effect:
Magicians and spectators are free to write their favorite illustrations.
The illustrations written by the two people are exchanged and stored in a sleeve that allows the inside to be seen through.
The audience has a picture they wrote.
Slowly shake the illustration written by the magician.
Then, the illustration gradually changes to something else, and it changes to the illustration written by the audience.
Looking at the sleeve that the audience had, it turned into an illustration drawn by a magician!