"A long time ago on a peculiar day, my mirror lured someone out of his bed...I do not know if the mirror was being mischevious...or malicious...perhaps it knew that the mysterious intruder had a role to play in my...project" --Yen Sid
In Disney's Epic Mickey, the sorcerer Yen Sid created a pen-and-paper world for his forgotten characters, held in an intricate model on a table, and accessible through a mirror. Mickey spills paint thinner on the pen-and-paper world, thus ravaging the world and creating The Phantom Blot.
Many years ago Yen Sid created a world for all his forgotten, rejected, and retired creations. He crafted an imaginative world full of different wonders that would appeal to anyone who would were to enter it. Yen Sid put the finishing touches on his world, ignorant of what Mickey was about to do this new world. By the time Yen Sid discovered the ruined world caused by Mickey creating the Blot (he didn't know about Mickey's identity yet), it was too late. It is unknown what happened to him afterward, and why he did not just throw away the model, or even try to clean and fix it as the years passed.
The observant reader will notice that "Yen Sid" is "Disney" spelled backwards, a mirror-reflection, if you will. Also, the unnamed sorcerer in the film "Fantasia" was nicknamed "Yen Sid" by the studio animation department.