Myotismon is dressed elegantly as a gentleman. His look and mannerisms are styled after vampires, and he has heterochromia: one green eye and one blue eye. However, in some scenes, he is depicted with two blue eyes.
Myotismon feeds on the fresh or deleted data of his victims, though he developed a taste for human blood during his stay in Odaiba, causing his victims to appear to have been afflicted with sudden anemia. His power is reduced in the sun, but he overcomes this by creating a fog around his location. He has some measure of telekinetic ability, such as halting and crushing a rock thrown at his head with his thoughts, and can deflect or dissolve almost any attack, unless they surprise him or are holy in nature; even then, most holy attacks aren't strong enough to do more than cause him severe pain. Even after being killed, though, he is able to revive himself as VenomMyotismon.
Before he encountered the DigiDestined, Myotismon was the one responsible for conditioning Gatomon into a loyal minion through harsh methods while she was Salamon. He also took hold of the castle where Gennai and the Agents had once worked, which contained a gateway to the Real World. When the DigiDestined arrived, he sent his minion DemiDevimon to try to keep them separated while keeping himself hidden, because he had learned of a prophecy that he would be destroyed by the Eighth DigiDestined Child. However, when Tai returns the group is able to start pulling back together despite DemiDevimon's best efforts, for which Myotismon frequently tortures him. When the children finally reunite as one group, Myotismon appears in person to attack, but although he initially held the upperhand against their Champion Digimon, he is surprised when the last child, Sora, finally awakens her Crest and causes Birdramon to become Garudamon, who manages to hold him off long enough for everyone to escape. He later enacts plans to enter the Real World, taking many of his henchmen with him, to find and kill the eighth child. However, the DigiDestined follow him, and for the next two days (August 1 and August 2), the two groups race to find the child. To his frustration, his minions prove unsuccessful in finding the child, and many of them are killed during their searching. On the night of August 2, Myotismon learns of Gatomon's relation to the Eighth Child. He then uses his power to isolate Odaiba from the rest of Tokyo through a thick fog screen, which also serves to isolate some of the DigiDestined and make it harder for them to stop him.
After identifying the Eighth Child, Kari, who was actually Tai's little sister, Myotismon easily overpowers the combined forces of the DigiDestined's partner Digimon. When Myotismon kills Wizardmon, Kari's Crest glows andGatomon digivolves to Angewomon, who gathers the other Digimons' power with Heaven's Charge and forms it into her Celestial Arrow. Like a mythological vampire, Myotismon is killed when Angewomon's arrows pierces him through the heart. Despite this, Myotismon is not yet truly defeated.
After Myotismon's apparent defeat, Gennai sends Izzy and the other DigiDestined an e-mail while they're still on the roof of the Fuji TV station. The ancient text of the prophecy was translated by Gennai as follows:
- The sky will be darkened by the wings of many bats.
- The fallen people will invoke the name of the Undead Digimon King
- And when the clock strikes the Hour of the Beast,
- The Undead King will reveal himself in his true form, as the Beast.
- Then angels will shoot arrows of Hope and Light at the loved ones of those they have been sent to protect
- And a miracle will happen.
After Myotismon's defeat, DemiDevimon revives him by collecting data to become VenomMyotismon. VenomMyotismon, no longer needing DemiDevimon, consumed him. Tai and Matt Digivolved Agumon and Gabumon into MetalGreymon and WereGarurumon to fight VenomMyotismon, but he easily beat MetalGreymon and WereGarurumon. Izzy then worked up a miracle to Warp Digivolve Agumon and Gabumon into their Mega forms, WarGreymon and MetalGarurumon. The other Digidestined combined their attacks and WarGreymon knocked the giant monster out. But VenomMyotismon then revealed "the beast within", which is another face that's actually the real form. The Digidestined's Crests then started to glow and held VenomMyotismon off while WarGreymon and MetalGarurumon destroyed VenomMyotismon, freeing the humans from his spell.
However, after VenomMyotismon's defeat, Myotismon's spirit lived on and possessed Yukio Oikawa. When Oikawa and the kidnapped Dark Spore children arrive in the dream dimension instead of their intended destination of the Digital World, Myotismon appears in Oikawa's shape to mock him, before fully exiting his body and leaving him unconscious. He materializes in his new, more powerful form of MaloMyotismon, then tests his new powers out by torturing and killing his own minion Arukenimon, leaving Mummymon in horror. Enraged, Mummymon attacks MaloMyotismon, but he is melted to death with MaloMyotismon's Crimson Mist. The second generation of the DigiDestined are initially too afraid to fight MaloMyotismon, but just as Davis helps the others to muster up their courage, MaloMyotismon uses his Mental Illusion to entrap each DigiDestined in a personal prison of their fantasies. Davis, however, is able to tap into the powers of the dream dimension, both freeing his friends from their own mental prisons, and showing them how to have their Digimon partners incarnate in each of their forms all at the same time. With this small army, the Digimon are able to blast MaloMyotismon away and tear open a passage to the Digital World. However, as they pass over, their partners' additional manifestations dissappear, and MaloMyotismon returns, having grown even more powerful by returning to the Digital World and feeding on the darkness both there and in the Dark Spore children. Just as all hope seems lost, a miracle occurs and the DigiDestined from all over the world use the light from their Digivices to empower their Digimon partners present in the Digital World, while the DigiDestined are able to help the Dark Spore children overcome their negative emotions and embrace their dreams, allowing them to become DigiDestined with their own partners and Digivices. All of the DigiDestined everywhere unleash the light from their Digivices on the now weakened MaloMyotismon, reducing him to a cloud of darkness. They then direct their light towards Imperialdramon Fighter Mode, who channels it into a massive blast that destroys MaloMyotismon once and for all.