We'll have the nitty-gritty below for those who like details, but for a quick look at how Theros Beyond Death Collector Boosters are bringing Theros to life, well, here you go: And, for the detail oriented, here's a less-pretty bullet-point list for what contents can fall in which slots
Title: Opt, Quantity: 3, Collected Printings [123, 456, 789] This way, we could track quantity at the title level while keeping a list of "unlocked" printings that the player can use
Modified is more of a nice bonus for doing something you were already going to do, rather than it being something you would build around specifically
Hopeful Initiate Training makes Hopeful Initiate a nasty threat that punches above its mana cost, then you can cash in the counters to remove dangerous permanents
With its disguise ability, you get to exile a bunch of other creatures from the battlefield and graveyard, both yours and your opponent's stuff
Gaining life after that point wont let you choose a target with a higher mana value.