Around the time of Modern’s inception, U/W/R Delver was one of the best decks. There’s a litany of cheap, viable counterspells, efficient threats, and great removal. Delver of Secrets dominated Standard for a long time, so it was no surprise to see it ported to Modern.
That deck kind of died off but has seen a recent resurgence with U/R Delver, eschewing the white completely. However, durdling around with Young Pyromancer is probably worse than casting Geist of Saint Traft, one of the most underplayed cards in Modern at the moment. Geist is difficult to kill, gives the Delver decks a heavy hitter (think Ball Lightning or Fireblast in Sligh), and provides the much needed reach to close out games where they’ve almost stabilized.
Figure of Destiny was underplayed, as Steppe Lynx was viewed as better at the time. Whether that was true or not is debatable, but Figure is a much better topdeck on turn 4 or 5. Mana Tithe is another exciting addition, as Modern decks are built to maximize their mana every turn which Mana Tithe punishes. If they play around, they’re slowing down their own game plan, so Mana Tithe often “works” even if you don’t draw it.
The combination of cheap counterspells, efficient threats, good removal, and a little card selection is a strong core, but the specifics depend on the metagame. No one has tried to find the specifics in a while, but Baba123 seems like he’s onto something.