With the "Devotion to Darkness" deck, your primary goal is to assemble many black permanents to increase your devotion to black—the number of black mana symbols in the mana costs of permanents you control.

You'll want to play defensively in the early game to keep your creatures alive and counting toward your devotion. Gray Merchant of Asphodel is one of the most powerful devotion effects in the deck, so it's a good strategy to hold it until you have many other black permanents on the battlefield. Abhorrent Overlord is a powerful way to turn your devotion into a game-winning army of fliers all by itself.