We get three to four full 'Standard' sets annually (about one every three months) and a varying mix of smaller sets - usually focused on specific formats, or revisiting a popular past setting with additional cards
Before Griselbrand, there used to be room for one oddball choice , like Sheoldred for long-game advantage or a Platinum Angel to stop combo decks that don't interact with the battlefield, somewhere in your 75
Ive seen posts explaining how to game this system, but Im not tech-savvy enough to know if its real or not
Madness Songbird, Sonic Screamer 2.0%inclusion 3 decks 147 decks Doctor Doom, King of Latveria 0.6%inclusion 2 decks 363 decks M.O.D.O.K
The other reason Wizards of the Coast created the Book subtype could be for strictly flavor reasons
Does it reveal a creature that costs 3 or less