Demons are a creature type most strongly associated with black mana, imposing creatures, and powerful abilities carrying appropriately sinister costs. Demon decks commonly use life, creatures, or other resources to obtain effects far above the normal rate.
Shadowborn Apostle can sacrifice an entire suite of Apostles to summon a Demon directly from your library, while Be'lakor, the Dark Master rewards a Demon-heavy battlefield. Liliana's Contract can even win the game for controlling four differently named Demons.
