The secret key enables you to get 5 special forms of rotom. Once you have cleared team Galactic out of Eterna City, go into their hideout (The one behind the trees that you cut). Right when you go in,go to the top left corner of the room, (Space between yellow and black thing and wall.) Press A. It will unlock a secret room with 5 appliances (Probably Fridge, lawn mower, Fan, Toaster and Washing Machine, I think) Go up to the one you want press A and your Rotom will take form of the appliance.
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.