At deviantart I made my idea and some kind of thing I hope to get.
When Celestia and Luna were prepared to go to their home, "he" showes up again. Nobody can defeat "him". So Celestia and Luna tried to blast him to the shadow world, but they are not strong enough and when he almost escapes again, Discord helps Luna and Celestia and defeat him. Celestia, Luna and Discord trow "him" in the shadow world, with consequence they will be trapped too. After a couple days it was Cadence who began to make plans with Twilight how to rule Equestria, now that they are the rulers.
http://fav.me/dalas10