You play as a child called Junior who enters an online virtual reality MMORPG called "Digimon Online", which is run by the "MAGAMI" corporation. A terrorist attack on the Internet traps Junior and his friends inside the game and he sets out to stop them with his Digimon partners.
Unlike past Digimon World games, battles against wild Digimon are random and the battle system although turn-based is very different from Digimon World 2, the most notable distinction is battles are one on one instead of three on three although you may tag in a different Digimon, battles also feature three types of digivolution; normal, Blast, and DNA digivolution.
Junior returns to the Amaterasu Server to defeat the final two chiefs, and gains access to Amaterasu City. He leads a fresh attack on the Amaterasu Admin Center, leading to the MAGAMI President being defeated. Junior then uses the central computer to destroy Destromon, before returning to Asuka to ask Airdramon to help him in lifting the virus which is affecting most of the players by transforming them into Oinkmon. Before long, the Oinkmon virus returns and strikes most of the players, with only Junior and Kali surviving untouched. Junior is challenged by an entity calling himself Lord Megadeath. Junior then travels to a military satellite, Gunslinger, to challenge Lord Megadeath. Lord Megadeath is defeated, but succeeds in his project of creating Snatchmon. Snatchmon absorbs Lord Megadeath and merges with the Gunslinger to become Galacticmon. Junior defeats him.
Three months later, Junior returns to the Amaterasu Server, where, as is revealed in the PAL and Japanese versions of the game, four new Server Leaders have been established and Kurt is the new MAGAMI President and World Champion.
You only fight bosses multiple times in the PAL version, Digimon World 2003, with Bulbmon as an exception.
Vemmon resembles a small alien, with two-fingered hands and reverse-jointed legs. Its whole body is a shade of purple, its helmet slightly darker than its torso. Vemmon's eyes are hidden by a black visor on its helmet, which completely covers its elongated head. A chain is attached to its neck for some unknown reason.
Vemmon, in the game, at first appears to be very weak. Its basic attack is relatively harmless, but has the annoying side-effect of stealing your Digimon's MP, preventing them from using special attacks. This means that Vemmon is somewhat of a vampire.
Vemmon's true power, however, is far more incredible. It is an artificial Digimon, created by humans as a multi-purpose weapon. Vemmon have the unique ability to combine their matrix data with technology, allowing them to turn themselves into a living embodiment of the machine they assimilate. In the game, only two ever achieve this, and both were ultimately destroyed. Late in the game four Vemmon fused inorder to combine their matrix data to digivolve into Snatchmon, which is capable of completely absorbing other forms of life.
Vemmon also had an ability to turn humans into Oinkmon, a pig-like Digimon of little use or importance. After the destruction of Galacticmon, it is assumed that all Vemmon are either freed from the control of their corrupt human masters.
Snatchmon is an antagonist. It resembles a purple humanoid, with a large visored helmet and a thick, curling tail. It broke free of its master's control and absorbed him after he refused to be a slave to anybody. Snatchmon claims to be the most powerful Digimon ever, and given his ability to merge his data matrix with technology, this may very well be true. After a short dialogue sequence, Snatchmon fuses with the Gunslinger satellite and becomes the mighty Galacticmon, the final boss of Digimon World 3.
Snatchmon's attacks are not known, but he is shown to absorb other digital lifeforms to further sustain himself.
Galacticmon is an incredibly huge cybernetic Digimon, resembling some sort of spacecraft. It is formed after the Gunslinger satellite is merged with Snatchmon and given life. Galacticmon's head alone towers over even the largest Mega Digimon, and during one cutscene it is shown in orbit above Earth, further adding emphasis to its sheer size.
Galacticmon appears to carry at least two giant missile silos in place of legs. Whether these are engines or indeed weapons is unclear. Galacticmon's tail contains a smaller head at the tip, and the tail is lined with solar panels which were once the power source of the Gunslinger. It also carries the Gunslinger's ultimate weapon, the Ragnarok Cannon, but this weapon appears to be significantly weaker than in its original state.
It appears to have a maintenance system including a skeletal metal hand which is uses to attack and block with during the fight against the head. It is not know whether the hand simply floats in space detached from the main body of the Digimon or whether it is actually connected, because it trails off into space behind the main body, where the back of it is shrouded. Also of note is that no matching right hand is visible during the fight.
After the final battle with Galacticmon, it explodes and falls to Earth as a meteor shower. Galacticmon's true plan was to merge with planet Earth to become Gaiamon.
Long believed by characters of the game to be unstoppable in every way, its only weakness was discovered by the game's protagonists after defeating its controller. They shut down the terrible machine before it could completely destroy the city it was attacking, and the monstrous Digimon self-destructed.
It is impossible to fight Destromon in the game, as it only appears in cutscenes.