A human sings along to "We Will Rise Again" while in Equestria, Discord is being banished. And as the human sings 'Let the chaos come' Discord is banished to earth.
Princess Celestia's best student, Sunset Shimmer loves to read books. She thinks of friends as a waste of time. She tells Celestia exactly that when the Princess Of The Sun tells her to make some friends.
In S9, After King Sombra's horn was found in the Crystal Empire, the princesses have decided to resurrect him and reform him. The pony to reform him will be none other than... Fluttershy!