There is no such thing as a Sweet Key, if you mean the Secret Key that is used to find the 5 Rotom Forms you had to download it via WFC when the event was, it's over now.
the game of platinum
The suite key is well hidden. When you enter the resort area from Pastoria, go left one step and it should be there. If not, use your item finder in front of the door and it should react.
Go into Eterna forest at night and Gardenia should be there. Go past the trees and into the Old Chateau and there will be a TV in one room. Thump the TV and Rotom will come out.
pikachu
You can use the move sweet scent.
It is the warehouse in veilstone city.
It's exclusive to Pokemon platinum version.
In diamond, pearl and platinum version you get a key from a trainer and you go to route 209 and near the lake threre will be a broken stone tower and you put the key in.
Its Wormadam! You have to let it evolve from a Burmy which you can catch by Sweet Honey Trees.
give him a secret key the different secret key the different rotom
You cannot get the secret key in pearl or diamond version. It was only available for a limited time via mystery gift on platinum version from June 2009 to July 2009. So, it is now impossible to obtain even in platinum version. Sorry, but you lucked out.
the game of platinum
http://www.neoseeker.com/Games/action_replay/
no only codejunkies.com which hasn't got it out yet
You can't, Mewtwo is not available in Platinum.
vulpix is not in Pokemon platinum version.
Yes creselia is is in Pokemon Platinum.