Digimon World 4
"It's up to you to save the digital world!" Digimon World 4 is an action role-playing game loosely based on the movie "Digital Monster X-Evolution", which was only released in Japanese. You start as either Agumon, Veemon, DORUmon, or Guilmon, and can transform into 12 others by completing missions for creatures called "Digi Elves" and earning them as rewards for your work - there are 16 playable Digimon in all. Defeat enemies, earn bits, and equip your Digimon for battle.
Story
The Yamato server has disappeared after the X virus attack and the Doom server has taken its place. It's up to you and up to 3 of your Digital Security Guard (D.S.G.) friends to infiltrate the Doom Server, find the source of the virus and fight the infection before it can infect the Home Server. You'll venture into the Dry Lands to stop the spread of the virus, into the Venom Jungle to prevent the launch of the Dread Note, and then into the Machine Pit to destroy the final boss. After you finish the game for the first time, you'll unlock the hard mode, in which the enemies are stronger, but you'll keep all your levels, equipment and digivolutions. If you manage to do it again, you'll unlock the hardest difficulty level, "Very Hard".