That lets you turn things like Darksteel Plate or Blackblade Reforged into instant-speed removal
Players enjoyed the opportunity to get multiple rares, having a guaranteed foil slot, having an opportunity to open a card from The List , getting an art card, etc
Honorable Mention #5
It's been a part of the game since the very first set ever released
25th Anniversary Rarity Collection II packs have twice as many Ultra & Secret Rares per pack, which gives you twice as many chances at luxury rares per pack (Quarter Century Secret Rares, Prismatic-style Ultimate & Collectors Rares, and Platinum Rares)
While Ratchet Bomb isnt a Modern staple, it does see play, often in colorless decks lacking removal options, as a Karn, the Great Creator tutor target or in mono-colored decks that cant easily power up Engineered Explosives as an answer to Urza's Saga tokens