These will be easy-to-complete tasks like Cast 30 White or Black spells or Play 25 lands
Additionally, while this card may demand a rather steep mana cost, as Demons are rather costly, this spell can be strategically cast once you've built up your board with a few Demons, ideally catching an opponent or two who'd over-committed to the board off guard
Additionally, they seem to have a high volume considering they are a more nicher subset (500 sold a year on average)
Marketing gimmicks are fine, but Wizards should know better than to act like sticking unique Secret Lair cards on "The List" is going to solve potential supply issues or do much to minimize the risk of printing unique cards in time-limited, potentially low-supply products
What it didnt pioneer was great card backs
The 6-year-old me that I had put away for safe-keeping all those years ago came rushing back to the front of mind