Yen Sid is Disney spelled backwards.
In the game you can unlock wearable costumes for Mickey which are The Sorcerer's Apprentice from 1940s "FANTASIA", the brave little Tailor from 1938s Mickey Mouse Cartoon "The Brave little Tailor", Steamboat Willie from 1928s Mickey Mouse Cartoon "Steamboat Willie", Firefighter Mickey from 1935s Mickey Mouse Cartoon "Mickey's Fire Brigade", Touchdown Mickey which is inspired by the 1932 Mickey Mouse Cartoon "Touchdown Mickey", Builder Mickey which is inspired by the 1933 Mickey Mouse Cartoon "Building a Building". Oswald's unlockable costumes are Oswald's Track Runner costume which might be inspired by situations in Oswald's Cartoons where he is running from danger, such as the Knight duel in 1928s "Oh, what a Knight" or in 1928s "Lost in Africa" where he gets chased by wild animals. Oswald's Knight armor is inspired by the 1928 Oswald The Lucky Rabbit Cartoon "Oh, what a Knight", he doesn't wear the armor in the Cartoon. Oswald's Mad Doctor costume is based of the Mad Doctor from the 1933 Mickey Mouse Cartoon "The Mad Doctor" whom Oswald had connections with due to his hatred and jealousy of Mickey. Oswald's Tron costume is inspired by Disneylands Tomorrowland and based of the 1982 Movie "Tron". Oswald's Gremlin costume is based of The Gremlins from the Movie based on Roald Dahls first book "The Gremlins" from 1943, the movie was in concept-phase by Walt Disney and Roald Dahl and was once planned to be part of the 1949 Package film "The Adventures of Ichabod and Mr. Toad" which was then called "Three Fabulous Characters".
In the extras you can watch the first Silly Symphony "The Skeleton Dance" from 1929 in its fully original form.