Which gaming marketing campaign was the first to use an alternate reality game (ARG) that involved millions of players solving real-world puzzles before the game's release?

In the highly competitive gaming industry, marketing campaigns can make or break a game's success. Some campaigns become legendary, transcending the games themselves to become cultural phenomena. This trivia question tests your knowledge of one of the most innovative and influential marketing campaigns that revolutionized how games are promoted. Do you know your gaming history well enough to identify this groundbreaking campaign?

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I Love Bees (Halo 2)
The Beast (A.I. Artificial Intelligence)
Portal 2's Potato Sack ARG
Why So Serious? (Batman: The Dark Knight)