Potential 12 win paladin deck. Go 6-0 with no difficulty at all, then get three guys who do stuff like this...
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Loss #1 Servant of Yogg Saron into Burgle into Coghammer. Spellslinger into Deadly Poison...
Loss #2 Opponent topdecks lightning storm, followed by Hogger and Ragnaros topdecks.
Loss #3 Opponent turn 1 plays coin/darnassus aspirant. Turn 2 he kills my 2 drop (I have sword of justice in hand I'm going to kill darnassus with) and then plays Earthen Ring Farseer on it. Turn 3 I play sword of justice. Opponent plays Dark Iron Dwarf, goes face. Turn 4 I play senjin. He plays claw, trades earthen farseer and face into it, plays mark of yshaarj on darnassus, goes face for 8. I play 5/5 frostwolf warlord. He goes face again, and plays volcanic drake. I play enter the coliseum, and trade my warlord into the drake. I'm thinking there we go, I've stabilized. I have only 7hp left, but I have lots of cards in hand and he's only got two. He topdecks kobold geomancer, and plays two living roots to the face, shapeshifts, and it's over. FML
Most of my six wins were facing decks like that, too. Fortunately most players in the arena don't know how to play :p