May I offer my take on this idea?
I've had quite a bit of time to think about this combo because I love the idea. And I love how amazing Heartless Summoning can be when used in the right place. Hell, having multiple of them in play with my idea isn't even a bad thing.
Alright, so the whole point of the deck is to combo off, yeah? Well, that's pretty easy. So, we're already in black and red. My plan is to make it Grixis. Because, well, blue just has the best ways of putting combos together. (Insert name of almost any combo deck here). See? Told you. Back to the deck. You add blue because, well, combo finding and such. But lets add another layer to the combo. Two more cards. Myr Retriever and Bitter Ordeal. Yeah. The point of that is that, with a single Summoning in play, you can cast the Retriever for free to kill it. Then you cast the other for free and get the other one back. And you repeat this process until you have enough Gravestorm count to mill them with Ordeal.
So, now we have five pieces of the combo. Heartless Summoning, Myr Retriever, Bitter Ordeal, Grinning Ignus, and Banefire. (I'm replacing Comet Storm and Devil's Play with Banefire because it's ultimately the only one you want to play. Unless you yourself have counter spell backup.) So, I think we all realise Ignus needs something to help with the mana. Above was suggested Gemstone Array. This card actually does nothing to advance board state. All it does would be generate storm count. If you want to use Grapeshot, cool. If not, lets look at another option.
Mycosynth Lattice. A bit expensive, yes, but it does exactly what you need it to do. Also, you're going to be playing the control deck for a bit. So what's wrong with grinding it out for six or seven turns to get this thing out? So just play the control thing and wait around until you get what you need.
On to what you could use in the deck. Well, things that are colorless and can give you an advantage with Summoning. Immediately my mind goes to Solemn Simulacrum. A 2 cost 1/1 that gets you land and draws you a card. I see no downside to the sad robot.
You could run a one or two-off Sphinx Summoner. It can acquire another Retriever if you need it.
Any other creatures that are good and can be abused with Summoning are amazing. Can't think of any off the top of my head. So on to a control package.
Faithless Looting - This card will literally start your Retriever combo without you having to do anything. You draw two cards, you discard a Retriever and something else. Boom. So it begins. Also, you draw two cards. I see no drawback.
Remand - Because card draw and a hard counter.
Mana Leak - Because it's really good.
Sleight of Hand - It's like another version of Looting without the discard.
Inquisition of Kozilek -Discard is pretty good. Provides decent early control.
Spell Pierce - Still one of my favorite counters. Good early and mid game.
I feel like that's really just the basics of the deck.
The goal of it is to either get the Retriever combo or the Ignus combo. Granted, dropping Ignus combo would just make the deck probably a lot faster, having it in there just provides another win condition. Which is nice.
Anyway, my opinion on it.
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