It has a low casting cost, and since many infect creatures are cheap to cast, it's likely you were able to get a few infect counters on your opponents, allowing for Yawgmoth to begin using its proliferate ability to add on more to them
Most players are just testing the waters and learning the cards, so we're still far from knowing what's good and what's bad
Print them yourself, of course
There's also other staples like Strip Mine and Scavenger's Grounds that I'll always make room for
With eight Set boosters, which include fancy alt-art cards and cards from The List, you'll also get four borderless scene cards of Frodo and Gollum in Mount Doom, a spindown counter, a bundle of basic lands to help make your deck, and a storage box to keep everything in