Faithless Looting started off in Modern as an enabler for graveyard-based combo decks. Dredge and Goryo's Vengeance decks needed the combination of card filtering and a way to get key combo pieces into their graveyard, and Faithless Looting provides those two things more efficiently than any other card in Modern. However, the fact that it inherently creates card disadvantage made it anathema to pilots of fair decks that care about raw resource count.
But since the emergence of Mardu Pyromancer, we've seen that having enough good cards to discard, mostly Lingering Souls, can make Faithless Looting a potent tool even in a deck that looks to attrition its opponents. Faithless Looting is the card that makes that deck tick, and has since been recognized as one of the most powerful cards in all of Modern.
The only natural next step is to see if we've been missing out on the card in other decks. Ben Friedman has had success adding it to his Grixis Death's Shadow list, taking it to the top 8 in Grand Prix Las Vegas, and today's featured list is yet another home for it: Temur Delver.
A classic tempo deck, Faithless Looting performs a number of tasks here, from acting as another hit to flip Delver of Secrets, a cheap sorcery for Young Pyromancer, and a way to fill the graveyard for Hooting Mandrills and Traverse the Ulvenwald. There are no flashback cards to discard, so you're always going to be down a card, but in a tempo deck that loss of card advantage isn't a big issue since you're trying to end the game quickly and that generally means having an unused card or two in your hand.
Moreover, this deck wants to operate on a very low land count, and any land after the third can be easily discarded at little cost. What's important is that you find the cards you need to shut your opponent down, whether that be Lightning Bolt against Humans or Spell Pierce against Jeskai Control, and Faithless Looting does that better than the blue cantrips.
Delver decks have had a tough go of it in Modern. Without the more powerful disruptive elements of the Legacy variants and facing a higher density of cheap removal, the 3/2 flier is hard to protect and the strategy as a whole gets shut down more easily. But Faithless Looting gives you a way to go longer and dig toward more threats when your opponent answers the first wave or two, so maybe the secret to making these decks work has been right in front of our eyes all along.
It certainly wouldn't be the first time.