Instructions
Scan Koromon data in Limit Valley. You will need at least 100 percent scan data, but higher percentages of scan data will create a Digimon with stronger stats. Obtain scan data by encountering Koromon in battle. Once you have over 100 percent, go to your Tamer Home and start the DigiLab PC. Select "Digiconvert" from the menu and "Find Koromon" on the list. Hit the A button and select "Yes" to convert the scan data into a Digimon.
Raise your Koromon to level seven, then digivolve it to Agumon. Bring your Koromon into your party and take it into battle. The easiest way to raise levels is to set lower level Digimon as Relief, and use higher level Digimon in the main party to fight more difficult enemies. When your Koromon has reached level seven, open the menu with the X button. Open the "Digimon" menu, select your Koromon, and choose the "Digivolution Route" option. Highlight Agumon in the digivolution diagram and hit the X button to open the menu. Select "Digivolve." Press "Yes" to confirm and Koromon will digivolve to Agumon.
Level up your Agumon. It is best to do this in areas with many dragon-type Digimon, since you will need 280 dragon-type experience points in order to digivolve it. Dragon EXP is gained by defeating dragon Digimon like Agumon and Koromon in Limit Valley. Once it has 280 dragon EXP and reaches level 18, you can digivolve it into a Greymon using the same method you used to make Koromon into Agumon.
Raise your Greymon to level 34. You will also need 3000 dragon-type EXP and 70 percent Friendship. Higher-level dragon Digimon will give you more EXP than Agumon and Koromon. Battle Digimon like Greymon and Tyrannomon in Task Canyon, Cyberdramon in Access Glacier, or Vermilimon in Proxy Island. To raise Friendship, you must win battles with Greymon in your Party. Once these requirements are met, digivolve Greymon into Metalgreymon.