Myotismon, or Vamdemon in the original Japanese, is a sinister, Vampiric Digimon with a sadistic streak a mile wide. Myotismon treats his underlings awfully, having taking Gatomon in when she was young and abusing her until she was a killing machine. When his henchmen fail him, he eagerly destroys them. When two harmless minions couldn't bring themselves to harm children, Myotismon killed them on the spot. When he invaded Tokyo, he proceeded to destroy much of it and held a number of children captive to identify the final child connected with Gatomon. He made it clear if it took too much time, he'd simply kill them all. Myotismon also proceeded to attack multiple young women and drain their blood, causing an epidemic through Tokyo. Any minions he hadn't already killed were cannibalized to fuel his Mega transformation. When he was thought destroyed, Myotismon's spirit survived to return as the final villain of the next season. Using a man named Oikawa's sadness and despair to make him a pawn, he proceeded to consume him from within and upon manifesting anew, Myotismon repaid his perfectly loyal ally Arukenimon by sadistically torturing her to death and killing Mummymon when he tried to avenge her. With a near unparalleled sadistic streak, Myotismon proved he was one of the vilest monsters in the franchise.
Piedmon is the leader and the most powerful of the Dark Masters, leading them in their conquest of the Digital World. A psychopathicMonster Clown, he enjoys toying with his victims before finishing them, in contrast to his more straightforward associates. Reducing his territory to a barren wasteland, he monitors the actions of his fellow Dark Masters and the main cast, allowing his allies to die without ever interfering. He participates in the murder of Pixiemon with the rest of the Dark Masters, kills Chumon himself, nearly kills WarGreymon, and then transforms most of the Digi Destined and their Digimon into keychains, which he toys with as he hunts the two youngest members of the team down, intent on keeping them all trapped as toys, forever. He's eventually revealed to be The Man Behind the Man to every major villain in the show, from Devimon through fellow Complete Monster Myotismon, and their actions and those of the other Dark Masters can all be laid at his pointy-shoed feet.
The cowardly, bespectacledscientist, Akihiro Kurata, is the single most despicable human being to appear in the franchise. Planning on committing genocide on Digimon due to nothing more than a petty grudge while conquering the world, Kurata created the Gizumon that would kill Digimon and stop their natural reincarnation cycle, which he first unleashed upon a noble Digimon who had been a surrogate father to the boy Ikuto. Kurata's reaction to Ikuto sobbing over his father's loss was cruel, hysterical laughter. Kurata then created a weapon to kill thousands of Digimon in a single blast and blackmailed one of the humans into working for him by threatening to murder his sick sister, before experimenting on said sister. Kurata's hatred extended to awakening a monstrous demon and attempting to merge with it to obliterate everything he saw as an enemy.
Tactimon is the one leader of Lord Bagra's armies with no positive or redeeming features about him. Not only is he responsible for rounding up several good Digimon into labor camps, including Cutemon's parents, he was prepared to torture Mikey, a child, to death instead of the quick, painless execution he could have ordered. As if that wasn't bad enough, he's a full follower of the We Have Reserves mantra and has no compunctions about sacrificing his own subordinates for the sake of maintaining his supposedly perfect battle record. This practice disgusted his follower Dorulumon enough to make him defect from Tactimon's side. Once he got out into the real world, he proceeded to lay waste to the area in hopes of getting his enemies killed and destroying what they valued. Shortly afterwards, he attempts to murder Mikey, Angie, and Jeremy with his bare hands. When it comes time for him to do battle with his enemies, all he can feel is pure excitement over the thrill of combat and bloodshed.
Another example from the same series is NeoMyotismon (NeoVamdemon), an Expy of Adventure's Myotismon and the second of DarkKnightmon’s Death Generals. The ruler of the Vampire Land, he was characterized by only one thing: an undying thirst for power. He possesses familiar spirits known as Evilvils that seek out the life energy of Digimon and give it to him. Not only does he fuse both his minions and his enemies into himself, but he absorbs a great number of innocent Lopmon living in his domain in order to gain immortality from their hidden power. During his battle with the Fusion Fighters, he attempts to absorb Christopher's partner, Metal Greymon, into himself as well, forcing Metal Greymon into an And I Must ScreamBody Horror situation.
The other particularly heinous Death General is Gravimon, ruler of the Canyon Land. He uses his own core as a way to take Christopher hostage, and then reveals himself as a sadist who uses his cables to torture Christopher and probe his mind. He revels in Mind Rape, mercilessly playing off Christopher's psyche until Christopher becomes broken enough to join him and obey his wishes. This set in motion the events that resulted in, among other things, the tragic death of Deckerdramon.