By now I'd say most players are familiar with the Infect archetype, having been around in Modern to some degree for years. But while most lists of the deck are G/U, there's a variant that swaps blue for black, with the main benefit being Phyrexian Crusader.
Going for speed, the traditional creatures in Infect are cheap and small, thus making them vulnerable to removal, so when cards like Lightning Bolt and Path to Exile are very popular, Infect can struggle. But Phyrexian Crusader is immune to much of the removal that is commonly played in Modern, so it gives the deck an added resilience at the cost of some speed, which isn't as important with the way the current metagame has lined up.
Phyrexian Crusader is also quite good against Humans, since most of their creatures are either white or red, and it cannot be bounced by Reflector Mage. They might have a Dismember or two in the sideboard to answer it, but you still have access to all the green protection spells. Their normal plan is to race against such a powerful threat, but the fact that Phyrexian Crusader blocks the largest ground creature the turn it enters the battlefield helps you turn the corner very quickly.
To gain access to Phyrexian Crusader, you have to make a few other concessions. Plague Stinger takes the place of Blighted Agent, which makes you weaker to creature decks that can easily block your other creatures, but also provides a higher density of infect creatures overall, so you won't mulligan as often.
And then there's the swap of counterspells for discard spells. Once again, I'd generally prefer the counters because taxing your opponent's mana on a key turn is an important aspect of the deck, but once you have a sticky threat like Phyrexian Crusader, having the discard spell to protect it from Supreme Verdict or a removal spell makes it a lot easier to land it on turn three and start racing, so the downgrade is rather small on the whole.
With the format slowing down a bit, this version of Infect is more attractive because you don't have to rely on speed. Phyrexian Crusader is powerful enough to dominate a battlefield, and access to black removal means opposing creature decks aren't goldfishing against you. You'll still win your share of fast games and that's important against combo decks, but you don't have to fear piles of removal as much, and that's a huge relief.