A couple weekends ago, I played Infect at the Team Constructed Open in Las Vegas. I teamed with the reigning SCG Invitational champion, Aaron Barich, and Legacy master Jody Keith. I picked up and played Aaron's physical deck that he used to win $20,000 and get his (thankfully not a Poison counter) 1/1 Soldier token with his likeness.
It'd been a while since I'd played Infect. I went into the tournament happy if I could shake off the rust and win half of my matches. With Aaron being a competent Infect pilot by my side, I figured he'd preemptively catch a minor mistake or two before I made one. This proved to be true. I put a Spellskite that I picked up from a transformed Thing in the Ice because he remembered it was a Horror while I didn't. My sideboarding and mulligan decisions were on point thanks to his second opinion. I ended up winning ten of the fifteen matches in the Modern seat, far exceeding my expectation.
What surprised me the most from the Las Vegas tournament was how much decks had adapted to deal with Infect. I lost a round to Tron, another to Ironworks, and another to Azorius Control. Previously I'd felt invincible in those matchups. I played against Arclight Phoenix decks four times and, outside of Ross Merriam's Open-winning version, I did okay for myself, beating the other three, which also came as a pleasant surprise.
So what changed?