just thinking here, how about a Mind Grind or some other cards from gatecrash like Consuming Aberration

This is made for Modern tournament play, those cards will just slow me down. Gatecrash isn't really made for Modern. This is my opinion but the set wasn't really that good anyways... there's maybe 15 cards I liked from it... 5 of them being the shock lands.

hmmm... 2 Duskmantle Seer in the sideboard might not be a bad idea actually.

Umm why is there no Hedron Crab s in this deck?

I thought about Hedron Crab a lot. I've restricted myself to 6 creatures, no more. It came down to Snapcaster Mage and Hedron Crab . Obviously I went with the Snapcasters. He is very good in a deck that runs 7 fetch lands though and I have contemplated switching him in for something. What would you suggest?

I would cut the Tome Scour simply because it is going to mill your opponent five the first time and five the second time. but Hedron Crab will get your opponent to mill at least three cards a turn and most likely six a turn, It is a fire and forget weapon, but Tome Scour is only good for one go

Witchbane Orb or Leyline of Sanctity ruins your day if your opponent manages to resolve one.

Maybe I missed something, but I don't see any way of dealing with that if they manage to hit the field.

You're correct about Leyline of Sanctity , I have put in 2 Demystify in my sideboard to deal with that. I would stick to B/U but I could not find a card that used my B/U to destroy artifacts/enchants. Witchbane Orb I'm not so worried about because it doesn't start on the battlefield.