Or Phyrexian Arena.
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Culling the Weak? This deck isn't hurting for mana, but it could turn a turn 2 Death Cultist or Fume Spitter into a Buried Alive for Three Bloodghasts, then Landfall them in.
Bear Umbra, by late game, it means more Eldrazi out per turn. My friend runs a fast Eldrazi deck like this, and Walking Atlas is a surprising help. Oracle of Mul Daya can get you a massive amount of lands pretty quick as well.