Cards like Narset of the Ancient Way and Sorin, Grim Nemesis benefit from discarding a split card since it deals damage equal to the mana cost
For more information on double-faced cards, checklist cards, delirium, madness, and skulk, please see the Shadows over Innistrad Release Notes
If all of the targets are illegal as Calamitous Tide tries to resolve, it won't resolve and none of its effects will happen
It is added to the 68 card Main Tribal Deck
That said, there isnt a control deck out there that should leave home without three copies of Aether Gust, with some in the maindeck, in order to defeat the top three decks of the format.
Shift is a great mechanic when used right, but Temporary Shift is a massive improvement in this case, as you can keep bouncing a huge threat back into your hand, and more often than not, your opponent is going to be helpless to stop you