Unfortunately you can only get it through a Nintendo event or a cheating device - there is no other way however there's this specific Secret Key event currently going on until May 12, 2009 which is no longer available and you need to do the following in order to get it:
Wi-Fi events are region-locked so only those players with the respective region's game can access the events if they're currently online. The US and Japan are no longer holding events as of right now for the Secret Key but Europe, Australia and New Zealand will be holding them soon and here are the details. For Europe, they'll be holding it via Wi-Fi from June 8, 2009 until July 19, 2009 and for Australia and New Zealand, their events are ones you have to go to since they're via wireless and here are the locations. First for people in Australia. For people who are in or near Queensland, it'll be available in Carindale June 27th and 28th and it'll be available at the Pacific Fair July 4th and July 5th. For people in or near Victoria, it'll be available in Soutland July 9th and 10th and at the Fountain Gate July 11th and July 12th. For people near or in New South Wales it'll be available in Chatswood July 18th and July 19th and at Parramanta July 25th and 26th. For people in or near Western Australia it'll be in Carousel July 4th and 6th. For people in or near South Australia it'll be in Marion on July 18th and 19th and for people in New Zealand it'll be available in Sylvia Park on August 8th and 9th.
You need to go to the Jubilife TV station and talk to a guy on the 3rd floor. Take the survey, and enter "Everyone happy" then "Wi-fi Connection" and you'll get Mystery Gift. Turn off your DS and turn it back on, but remember to save. Go to http://www.pokemon.com to get updates on when the Event will happen (then go to "Receive gift via Wi-fi connection" on the Mystery Gift menu which should be under "Options" now.
1. You can go to Toys 'R' Us. Download the Secret Key via Local Wireless Mystery Gift. Activation of Mystery Gift is not needed for local wireless downloads. This wireless event goes on until April 26.
2. Go to the male producer on the 3rd floor of the Jubilife TV station and tell him these 2 phrases "Everyone Happy" and "Wi-Fi Connection" - save and turn off the game. Start the game back up, go to Mystery Gift and select "Receive from Wi-Fi" and it should download into your game. This Wi-Fi event goes on until May 12.
3. Head to any PokéMart and collect the item from the guy in the green hat. It'll now be in your Key Items.
WELL IF YOU WOULD PAY ATTENTION THIS DOESN'T WORK SO DONT WASTE YOUR TIME
>:(
go back into the building near the end of eterna Forrest and the room will be there
P.S. all of the forms are the same they only have different looks and can learn a few different moves but there all electric / ghost
You go to the old chatau and use the key for the kitchen so u can change rotoms forms
You can't get rid of it unless you didn't save the game when they gave it to you. In that case you just turn the power off.
The event to download the key was over a year ago.
It's too late to get one now.
Unless you use Action Replay.
its a secret place
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secret key is the only 1 i know at the moment look on the Pokemon.com website to see how to get the secret key by beating either Jupiter or via wireless internet(wifi)
hes not in platinum:( try ruby
ActionReplay
You can only get the secret key in Pokemon Platinum
you need wifi do get it!
well you need the secret key for team galactics HQ
Already happening............
No, you can't mix records in Pokémon Platinum in order to get the Secret Key from a friend.
You can't get the Secret Key in Pokemon Platinum without Action Replay, unfortunately. You can get Action Replay from most major websites.
stop being a Pokemon playin douche
obtian the mystory event
The Old Cheatu.
give him a secret key the different secret key the different rotom
No you have to get it again.
check serebii.net for info on upcoming events for Pokemon Diamond,Pearl,Platinum.