The hottest deck in the Modern format could very well be Grixis Death's Shadow. This deck has many of the cards we expect to see from Death's Shadow variants that inflict life loss, including Thoughtseize and Street Wraith, but also lots of interactive spells and card advantage as well. Blue Death's Shadow decks have been gaining momentum for a little while now, and it has gotten to the point they may be more popular than the green-based Death's Shadow decks. Brad Nelson hit the nail on the head with this one.
Playing this deck is a lot like playing traditional Grixis Control, for those that have experience with that deck. There are lots of small decision like when to crack your fetch land, or which one-mana spell to cast, that can really add up. Since the deck has lots of card advantage, games aren't as much about racing the opponent but rather about surviving until you can take full control.
Affinity is a very close matchup. Kolaghan's Command and spot removal certainly helps, but sometimes they have an explosive draw like we saw in game one that is too difficult to match. In order to win, you really need to answer their first couple plays before playing threats of your own. After sideboarding, I believe you are ahead with the additional removal to go along with Ceremonious Rejection. In game three we played our way into a spot where our opponent needed to peel – and they found the Galvanic Blast in time – but the game was certainly interesting.
The other artifact deck we faced off against was pretty weird, and we didn't actually get to see that much of it. Hate cards like Chalice of the Void, Blood Moon and Ensnaring Bridge are good but we have enough tools to fight them. Decks playing all those hate cards might seem like a bad matchup for Grixis Death's Shadow, but it really didn't feel like that was the case. We were able to keep Blood Moon off the board though and Kolaghan's Command shined in this matchup as well.
The mirror should generally be a coin flip, but we learned how good the big delve creatures are here. Death's Shadow is actually much easier to deal with compared to the delve creatures because it dies to Fatal Push. It felt like a matchup that was about both tempo and card advantage, but also comes down to successfully managing your life total.
After playing with Grixis Death's Shadow, it is definitely one of the Modern decks that allows you to maneuver out of some very tough situations, but at the same time one small mistake can be the difference in a game. This is a good choice for players that don't want to play a true control deck, but also don't mind transitioning into that control role when necessary. The green-based Death's Shadow decks feel much more similar to Jund or Abzan than the Grixis version does. Since this deck plays so many versatile cards it is very difficult to hate out. We saw even the most hateful sideboard cards look pretty embarrassing when facing off against the artifact prison deck.
Currently I think Grixis Death's Shadow is the best deck in the format, though there are plenty of other decks that can compete against it. It turns out that counters and card draw go alongside Death's Shadow pretty well. Who would have thought?