How did players get event Pokémon in Generation IV?

Earlier generations ran events like a travelling show: you brought your cartridge to a store or a tour stop. Generation IV, the first online generation, moved the show onto Nintendo Wi-Fi Connection and split it into two kinds of gift, delivered through Mystery Gift. The first kind was a key item that unlocked a story already sleeping in your game.

Platinum received the famous set. The Secret Key opened Rotom's hidden room and its five appliance formes. The Member Card, distributed in Japan from December 1, 2008 to January 15, 2009 and in North America from August 3 to September 13, 2009, opened Canalave City's locked inn and the nightmare voyage to Darkrai. Oak's Letter, which reached North American Platinum games from September 28 to November 8, 2009, turned the end of Route 224 into a flower road to Shaymin.

The second kind skipped the item and handed over the Pokémon itself: film tie-in distributions, store giveaways and Wi-Fi gifts, like the movie Arceus of 2009 whose presence in HeartGold and SoulSilver unlocked the Sinjoh Ruins, or the Enigma Stone that arrived by Wi-Fi in 2010 and drew out Latios or Latias. The Pokéwalker joined in too, receiving whole event routes, Yellow Forest among them, as downloads.

And one Pokémon came by post from another game entirely: Manaphy, hatched from an egg earned in Pokémon Ranger. The full system's one famous failure is the Azure Flute, the Arceus item that was built, announced in code, and never distributed at all.