Tirek has returned, and he wants all of Equestria's magic. Twilight won't let him have that, and she is the final obstacle between him and world domination.
Discord finally escapes his stony prison, but he's got a proposition for Twilight. One that will either see him reformed, or as the ruler of Equestria.
The Crystal Empire has returned, along with its tyrant, King Sombra. It is up to Twilight to save the Crystal Empire, and she does exactly what is expected.