This is an aggro-control, or “tempo”, deck that plays efficient interaction to survive the early turns. It looks to grind out card advantage in longer games on the back of cards like Spellstutter Sprite, Snapcaster Mage, and Bitterblossom.
Kalitas, Traitor of Ghet
This is one of the best “fair” decks in Modern currently. It plays efficient disruption in the form of discard spells and Lightning Bolts to keep itself alive in the early game, while playing powerful threats like Young Pyromancer and Bedlam Reveler to generate card advantage as a game goes long. It also gets to steal the occasional “free win” on the back of prison cards like Blood Moon and Ensnaring Bridge.
Kambal, Consul of Allocation
This is simply a collection of reasonably powerful Modern-legal cards. Just some of the best spot removal, discard, and threats the format has to offer. It packs it all into a brutally efficient curve that allows it to easily keep up with the slew of linear decks that tend to see play in Modern. You can read some of my fuller thoughts on BG Rock on Gathering Magic here as well as some specifics on sideboarding with the deck here.