Things You'll Need
Instructions
Put Scyther in your six Pokémon party at a Pokemon Centre. If you do not already have a Scyther, they can be found randomly on Route 229.
Open the Pokemon menu, select Scyther and select "Give Item." Select the Metal Coat, then back out to the main menu.
Power on the second Nintendo DS console and insert the other Pokemon game. Get the second game's character to the nearest Pokemon Centre. Go upstairs to the trading area. Speak to the receptionist, who will prompt you to save your game and then send you into the trading room.
Repeat this process on the first DS console to bring your character and Scyther into the trading area.
Initiate the trade on the first game, and select "Scyther" for trade. Accept the trade on the second console. Wait a few moments for the trading animation to complete. The second console will indicate that Scyther is evolving.
Trade Scyther back to the Pokémon Diamond game.