Ever since I first opened a Vexing Devil and Treacherous Pit-Dweller, I knew there must be a way to abuse them. Here's my attempt at it.

Everything is very low-cost here, and the basic idea is to get a Torpor orb out as fast as possible, which makes the Pit-Dweller and Vexing Devil have no drawbacks at all. They become a 4/3 for R and a 4/3 undying for BB. In addition, the metagame seems to be in such a place right now that will cause Torpor Orb to seriously disrupt an opponent (it disables Snapcaster Mage, Restoration Angel, Blade Splicer... you name it).

Fume Spitter: a 1-drop that can make undying creatures last longer, kill weenie blockers, and/or be fodder for the Demonlord of Ashmouth if you can't get a Torpor Orb out in time.

Fling: In this deck, this is consistently a 4 to 6 damage instant for 1R. Can act as board control while activating undying to buff your creatures.

Vapor Snag: helps press the tempo advantage of dropping big creatures early, and can also be used to steal back a rogue Treacherous Pit-Dweller to your hand, if it was killed before you played a Torpor Orb.

Faithless looting: Dig as fast as you can, find Torpor Orb! Can be used to help fix mana, too. Doesn't really have a drawback if you're throwing away excess Torpor Orbs or another flashbackable Faithless Looting. These are the same reasons that Think Twice is in the sideboard (didn't quite make the main cut)

Sideboard definitely needs refinement. Comments welcome!