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Heart Gold and Soul Silver: Changing Rotom Form
When you trade Rotom to Heart Gold and Soul Silver you can still change it's form very easily. After you have access to Kanto, go to Saffron City and then go to Silph Co. Usually the elevator in Silph Co. is broken, but if you have Rotom following you as the first member of your party he will make the elevator work and take you to the basement of Silph Co.

Once you are in the basement of the Silph Co. building there will be five appliances you use to change Rotom's form.

Sprite
Form
Special Move
Appliance
Original
None
None
Fan
Air Slash
Fan
Frost
Blizzard
Fridge
Heat
Overheat
Oven
Mow
Leaf Storm
Mower
Wash
Hydro Pump
Washer