Only one copy of each card (except basic lands) is allowed
This is key so you can use its ultimate ability to return and cheat big artifacts into play that you may have milled or sent to the graveyard in other ways, or why not drop them directly from your hand for only the initial investment of your planeswalker
Even if her regular variant can be obtained at a much more reasonable price, Y'shtola's massive popularity in the Final Fantasy community comes at a steep price for the rare collector's booster variants
I frequently forget this ability exists, because its almost always overkill, but the card filtering is insanely useful for finding a way to close the game
For example, it's supposed to have a Bant "Tap and Untap" theme, right
Nobody wants to attack into this stupid artifact creature or spend a removal spell on something that drew you a card, so players will ignore you entirely