Flinthoof boar is a must. its a 3/3 for 2 mana almost always and can be played off of your emisarry. And it's still a 3/3 in the graveyard for varolz.
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I don't think Wydwen can block Thraximundar alone. When Thrax attacks his ability goes on the stack, and you would have to flash in Wydwen during attack step so she can block. Wydwen would be on top of Thrax's ability on the stack, which means she is in play when Thrax's ability resolves and therefore sacrificed.
I feel like Clarion Ultimatum isn't really worth it just to get 5 basic lands.