I've been piecing together a WGD deck and like the way this list is going. I really like the idea of using Piranha Marsh. Splash in a few crop rotations and this could be a viable kill condition. I could see this in Emperor and Chaos style tournaments too.  I've also found Misdirection to be a better counter card than Pact of Negation. It is a bit more affordable (money wise) than FoW and can do things like target an opponents creature or graveyard by redirecting a Swords to Plowshares or Ebony Charm.