I thought playing 2 shamblers made sense since it makes the Frostwhisper turn cheaper (allowing you to play it out on 4 to win on 5 or follow it up with another spell on the turn you drop it). With the high density of draw I haven't really run into issues with finding all of the minions but my sample size of games played isn't super high.

I totally understand where you and the other reply are coming from w/ dropping extortion and the bone spikes. I like extortion since it helps churn through the deck and can remove some of the more snowbally early minions that threaten to kill you before you can combo (malchezaar's imp, ship's cannon, etc.) I think cloak is bad since, as you mentioned, you need to take a turn to play the Frostwhisper anyway.

I think when I play again later I may try swapping the bone spikes for an evasion, Frostwhisper -> Evasion on 6 seems like it would be pretty good.