This is my first attempt to build a deck based in Heartless Summoning. For this deck, I need, mainly, two type of cards: bad guys thats strikes hard and something to allow me sacrifice the enchantment when I don't need anymore.
Myr Superion is a cool card in this deck, since with Heartless Summoning on the battlefield is a free 4/5 without drawbacks.
Priest of Gix, with the enchantment in play is another Dark Ritual, and without it, a method to play the Myr Superion.
Greater Harvester and Drinker of Sorrow are both nasty guys that allows me bury the enchantment.
Abyssal Persecutor its an easy call in a deck with many things that allow self destruct my own permanents, and with the Enchantment in play, is a 5/5 flyer for 2 black mana.
Lotus Petal, Claws of Gix and Executioner's Capsule provides all cheap permanents, ready to satisfy creatures drawbacks, like Greater Harvester or Drinker of Sorrow ones. Also, each one provides help in a concrete spot of the game. Lotus petal provides mana acceleration. Executioner's Capsule, creature removal and Claws of Gix is an extra method to sacrifice stuff, and gives me a little life burst.