It seems to me that the classic best reason to use black in Thresh has been access to Dark Confidant. With that out, you have Ghastly Demise as the only black card in the main. Is this new guy really good enough to lose things like Mage and STP or Bolt and Fire//Ice?

Black is imo currently a very strong color, but this deck is not really making use of its strengths very well. Instead of showcasing the best stuff like Deed, Hymn, Damnation, etc. you have Ghastly Demise. I'm not saying you should replace the demises with Hymn or something. They are there for a clear reason. But perhaps this deck needs to be seriously reworked when you consider what is going in and what is not being used at all.