I like this deck but it seems like a lot of the clutch cards have a high mana cost. Against a fast pace deck you might run into the trouble of not getting out the big cards before your opponent hits you for the win. I do like Leyline of the Void though.. that's a pretty interesting card and it seems like it'd work fantastically in this kind of deck.
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I think Drowner Initiate would be a good creature to put in here, because it's like Millstone but it'll offer some protection on the battlefield as well as cost less mana. Also, you should probably put Counterspells in here for some control over the opponent.