This deck is absolutely amazing. It was crushing it for Sjow today. Aggro and Control stand no chances with this deck. I'm not entirely sure of the mulligan. But I imagine its Wraths for Aggro, Wild Growth a must keep, Branching Paths to buff Spreading Plagues. Something along those lines.
Good luck ill be trying it tonight as well.
*UPDATE* From rank 8 to rank 5 with this deck no problem.
Mulligan against aggro? Wild Growth, Swipe, Spreading Plague, Nourish. Control? Wild Growth, Nourish, Dark Mire Moonkin, Swipe, Master Oakheart.
Hope this helps!