* Mystery Gifts are primarily obtained through wireless communication: You'd receive them via Nintendo Wi-Fi Connection (which is now shut down).
* There are no "secret keys" involved: Mystery Gifts relied on codes or events, not specific keys.
How Mystery Gifts worked in Pokémon Platinum:
1. Wireless Connection: You'd connect your DS to the internet (via Nintendo Wi-Fi Connection).
2. Mystery Gift Menu: Go to the "Mystery Gift" option in the game.
3. Receiving: You'd choose "Receive Gift" and the game would search for available gifts.
4. Codes: Sometimes, Nintendo would release specific codes that you could enter to get specific items.
Unfortunately, since Nintendo Wi-Fi Connection is no longer active, you cannot receive Mystery Gifts in Pokémon Platinum anymore.
If you're looking for rare Pokémon or items, you might consider:
* Trading with other players online: You could try finding players willing to trade with you.
* Using emulators: Some emulators allow for "save file manipulation" but this is considered cheating by many players.
Remember, always prioritize ethical gameplay and respect the spirit of the game!