This is what we in the business refer to as a “spicy one.” Death Cloud has been the pet card of many a brewer ever since it was first printed in Darksteel many moons ago. Few cards have the power to completely reshape the texture of a game in the way Death Cloud does, especially when paired with nonland, noncreature permanents that make mana so you can leave yourself in the best position to recover from it.
Historically, the permanent of choice has been Garruk Wildspeaker, but mana artifacts like Guardian Idol and Mind Stone also do a fine job. Solemn Simulacrum similarly leaves behind some value when sacrificed to Death Cloud, making it an ideal fit here. The other ramp elements, Gemstone Caverns and Simian Spirit Guide, not only help to power up Death Cloud but also enable Chalice of the Void, one of the most powerful cards in the format when cast on turn 1.
The recent addition to the deck, Kalitas, Traitor of Ghet, functions as an excellent finisher. Even if you sacrifice it to Death Cloud, you will be left with all the Zombies from your opponent’s creatures hitting the graveyard. Between it, Guardian Idol, and Mutavault, you should be poised to not only recover from a Death Cloud but to quickly end the game before your opponent has a chance to.
Death Cloud decks have historically shined in creature-oriented, aggressive metagames, yet Modern is being haunted by the specter of Dredge, a creature-based deck but one that operates on few lands and can kill you if you spend too much time setting up. Strategically this deck should not fare well in the matchup, but it has some quality tools that give you a chance.
In the maindeck you have Chalice of the Void, which can shut down Faithless Looting, Insolent Neonate, and Shriekhorn as early as turn 1, as well as Kalitas, Traitor of Ghet to stop Bridge from Below and drastically upgrade your sweepers from minor speed bumps to game-ending. And you have two copies of Bojuka Bog, which are an easy fit for a primarily black deck that can handle a couple of lands entering the battlefield tapped.
Despite these tools, I see this deck being behind against Dredge in Game 1. But lurking in the sideboard are four copies of Leyline of the Void, the absolute best card in the format against Dredge and one that this deck plays perfectly. Even if it’s not in your opening hand, you have the acceleration to cast it in a relevant timeframe, provided you have some of your other disruption to slow your opponent down.
Outside of Dredge, this deck is doing powerful things that should let it compete against the robust decks in Modern, and it offers a happy medium between prison, ramp, and control, so regardless of your preferences you will find something here that you enjoy.