I think in order for this deck to work, you can't just focus on the combo. Yes, you always want to see a T2 Waste Not and then a T3 Dark Deal. But if you don't draw the Waste Not, then what? What happens in game 2 when they board in all their enchantment removal?
For starters, I like Chasm Skulker. He is fragile as a 1\1 for 3, but he requires an immediate answer. They don't have it and he can become a huge problem. You cast a Dark Deal on T4 after the Skulker and now it's almost too late. He could be as large as a 6\6. And if they don't exile him, you have X squid tokens to deal with as blockers or attackers.
Next we have Fate Unraveler. Good by herself, she also excels when a Deal is cast because now your opponent is forced to draw X cards. Her 4 toughness also keeps her out of most cheap burn range. Although susceptible to enchantment removal, that's one less spell they can aim at your Waste Not.
Finally the Deal loads your graveyard up with spells- perfect for delving. Makes Tasigur, the Golden Fang super cheap, as well as Murderous Cut and Treasure Cruise. Gurmag Angler is also a maybe here because, although not as powerful as Tasigur and cost a few more mana, he is much easier on the wallet, and has the added bonus of eating Rhino's. Toss in a pair of Treasure Cruise to round out the card draw, and that's a bunch of delving.
There is a lot of delve targets in this deck, but the potential is there to go from no graveyard to a stocked graveyard. Rakshasa's Secret is a hidden gem here- obviously forcing a pair of cards to be discarded is a big deal by itself, but it also triggers Waste Not twice, and adds 3 cards to the yard for your delve. And of course your Dark Deal dumps cards in the yard by the handful.
Sign in Blood is good to keep your hand full early, but also adds utility late game. It can act as a 2 damage burn spell by itself, but with the Fate Unraveler it now does 4. Want a few more Waste Not triggers? Give them a couple cards and then hit them with a Secret.
Risen Executioner gives us some early, sustainable pressure, and the added ability to have him milled away with the Secret, or pitched to the Deal, and then just keep bringing him back.The delve cards in the deck allow you to remove other creatures in the graveyard to help keep his recur cost down. Also really good against the control match-up. As an added bonus, he makes your Zombie tokens from Waste Not 3\3's. If played out on curve with a T2 Waste Not, T3 Dark Deal, into T4 Risen Executioner. Pretty strong.
Hero's Downfall is just solid removal, and Murderous Cut is usually pretty cheap with the yard being constantly full. Bile Blight rounds out the removal- obviously good against the agro token decks.
The deck is lots of fun to play, and I highly recommend it.