It all started with a (in their minds) relatively innocent idea from the Cutie Mark Crusaders to get their marks. Oh, boy did they succeed. And, in doing so, they unleashed a change unlike anything yet seen on Equestria. It only involved Becoming One with the Sun, ancient rites, filling an empty gap in Celestia's stomach, mirror clones, and a whole host of other freakiness that pegs out the 'Whoa-o-Meter'. Great.

Now they, and everypony else are stuck dealing with a world where death is but an inconvenience save for old age; where odd transformations, merging, crazy experiments, and solving your schoolyard bullying problems by eating your bully for a few hours has become the norm.

Boy, they really managed to screw up this time.