I am playing with a similar build to this... i've found that Tiumph of the Hordes and Increasing Savagery help a lot in the end game as does the Revenge of the hunted. Replace something to get another Vampire nighthawk and definately a Necropolis Regent or two, Like the deck though, its a good build and should treat you well
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Blitz Hellion's might work for an end game, since you can keep other players mana down so they cant do much about them. Some mana ramp might speed it up and Leatherback Baloth might be a good early game. I like the deck though