I originally liked #$&*@!'s Thunder as more of a finisher - but it
has become a bit of a dead card in some games. Thrax does cost "like a million" but so does the Ultimatum - and though the Ultimatum is definitely better, if my control is working Thrax often just does more damage.
For my meta, I'd probably board Anathemancer. Shambling remains < Thunder, IMO, though I probably won't run either.
I like Infest because a lot of decks around here use Dauntless Escort. True, Fallout is uncounterable, but Infest is unpreventable. Besides, I've had people use Thought Hemorrhage targeting Volcanic Fallout before I even played one - just because my deck was part red. I'd start with Infest main. I guess it's a meta issue, for now, though...
Okay, so do you have any spare Thoughtseize?
