Get Rotom and Change Forms in Pokemon Brilliant Diamond and Shining Pearl

Light bulb: Rotom
Microwave oven: Heat Rotom
Washing machine: Wash Rotom
Refrigerator: Frost Rotom
Electric fan: Fan Rotom
Lawn mower: Mow Rotom

AntMag.NET

Rotom is an Electric and Ghost-type Pokémon that can only be obtained after acquiring the National Pokédex during the postgame. To find Rotom, you must visit the Old Chateau, located north of Eterna Forest, at night.

Upon entering the Old Chateau, proceed upstairs and through the central door at the back to reach a long corridor. Enter the first door on your left. You will find an old-school television that is turned on. Inspecting this TV will initiate a battle with a wild Level 15 Rotom. This is your only opportunity to catch it, so be prepared.

Be mindful that Rotom is a low-level Pokémon, so you may need to use weaker Pokémon in your party to avoid accidentally fainting it. Since Rotom is a Ghost-type, moves like False Swipe will not work unless your Pokémon knows Foresight or Odor Sleuth. Rotom also cannot be paralyzed by Thunder Wave. Utilizing Dusk Balls at night is recommended for a higher catch rate.

After successfully catching Rotom, you will also receive the Secret Key. This key is used to unlock a special room in the Team Galactic Eterna Building in Eterna City. Enter the building and go to the top-left corner, near the cupboards. Press the A button in the gap to reveal a secret door.

Inside this room, you will find five electrical appliances. With Rotom in your party, interact with any of these appliances, and Rotom will enter it, changing its form and adding the appliance to your Rotom Catalog. The Rotom Catalog is a key item that allows you to change Rotom's form at any time. You will receive the Rotom Catalog after Rotom enters the first appliance.

By inspecting all five appliances, Rotom will cycle through its various forms, and each corresponding appliance will be added to the Rotom Catalog: