GB deck featuring dinosaurs and, really, nothing else.  Not even good ones, Breaker of Armies notwithstanding.  Went 2-2-0:

Round 1: Bye
Round 2: 0-2 vs. RU Eldrazi control deck, which tapped down all my dinosaurs while pinging at my life total with flying creatures and nettle drone.  Also 3 copies of Sweep Away.
Round 3: 2-1 vs. WB allies based on valuable rally triggers.  When it came together it could gain tons of life off of indestructible creatures, but otherwise our creatures were generally bigger.
Round 4: 0-2 vs. RBc aggro allies, which could come out so quickly that our deck basically folded before it could get any dinosaurs in play, not that they would have had much advantage.

The big problem was forcing colors that proved to have extremely few ways to interact with the opponent, having gotten overly excited to play Baloth Null before evaluating whether we could build a well-rounded deck that included it.  Not only did we never draw one, in most games it wouldn't have even pulled it's weight.  It likely would have been better as a splash, like Drowner of Hope was, or even cut it entirely in favor of going white or red-green (the former was highly open, the latter had Mina and Denn, Wildborn and might have wheeled Relentless Hunter).