i think u a secret key before you can change rotoms formes
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In Pokemon Diamond and Pearl and Platinum which are the newest versions on the DS until the newer ones you catch Rotom after you get the national pokedex. Then you can transform him into different types.
Rotom can change forms in platinum
No trainer have Rotom in Pokemon Pearl, Diamond, or Platinum.
fist you need to have a rotom then get the secret key
tap the tv at night. it will get rotom out.