http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtg/daily/arcana/1424

The "Underworld Herald" deck combines aggressive swarms of creatures with devastating spells that destroy your opponent’s forces. Enchantment creatures and powerful devotion creatures give you a solid backup plan if your initial offensive can’t finish things off.

This deck features a mix of aggressive mechanics. Unleash lets you choose to have your creature enter the battlefield with a +1/+1 counter at the cost of not being able to block. Bestow lets you cast some of your creatures as Auras that turn into creatures if the target they are enchanting is removed. This gives you resilience against opponents who can kill your creatures. Abilities that count your devotion to black get more powerful based on the number of black mana symbols among the mana costs of permanents you control, including hybrid mana symbols like the one on Rakdos Cackler—perfect for a deck with only black cards.