This is mostly a midrange/control mono-shadow deck, like many others that came before it. However, the new set brought two spicy additions - At Any Cost, 6-cost Severin, and Spiritweaver. And since I decided I wanted Severin, that meant that I also wanted Karvet.
I have not been keeping precise deck stats. However, the rough stats I've been tracking put the winrate around 70% across 50+ games over several weeks. That suggest a pretty remarkable degree of consistency, especially since the majority of those games were during the tyranny of Rakano. And yes, this deck had a positive winrate even against pre-nerf Rakano.
I still have no clear idea what I need to do with the market. It's worked ok, but the only card I'm 100% sure about is the Malediction.
Another user suggested Induce Madness in the market; the reason for this is that the Piercing Griefs are considered to be Sacrificed at the end of your turn ... so every surge of Severin can equal a removal if Induce Madness is on your opponent (and if the Grief survives until the end of the turn). This does seem pretty good, so I added it to the market here. However, I should note that since adding it to the market, I have never once fetched it.
Side note: Makkar's Quiver counts as possible removal when you spellcraft it, but it really shines in the mid/late game. All of your Griefs become 4/1. I also had one game where my opponent just wasn't conceding, so I started buffing units with the Quiver. I think I had it up to +40-something per use when the opponent finally conceded. If you buff Griefs that then die, that puts a bigger attack unit into the void, which means the next application of the Quiver is bigger ... you can see how it snowballs. It's pretty awesome.
Lastly, there are some games where you need At Any Cost to go face for the win. It's a bit of a trick to identify those games (where your only chance of winning is a massive blast to the face), and then patiently bide your time to try to draw into it, or save it until it's fully active. It's not the most common situation in the world, but there have been a handful of games that would have been losses if I had not identified that as my only "out" and stuck to it.