Ogremon in "Home Away From Home," pictured on the right. Those eyes.
Raremon could easily come off as this. If Mr.Face raped a bionic manatee, this would be the result.
Myotismon in general. Venom Myotismon is even more due to his...eating habits...
Gatomon's life under Myotismon qualifies, and Wizardmon getting shredded by Myotismon, even in the edited version
Piedmon's, ah, "key-chain hobby." What makes it even scarier is his hunting them down one by one in a methodical and sadistic manner. Except for the fact he doesn't actually kill them, it's almost like watching a slasher killer hunting down his victims one by one...
Definitely qualifies. That episode literally gave this troper nightmares.
Machinedramon. The combination of his Creepy Monotone and the fact most of his dialog is composed of how much he enjoys killing people makes him one of the scariest villains in the show.
Machinedramon: Just what I was looking for, victims!
The penultimate episode, when Apocalymon pretty much deleted the Digidestined and their partners. That's got to be pretty traumatizing for a kid watching the show...
The trailer for the PSP video game adaptation. At first it's all bright and cheery and gives you a real nostalgia kick. Then the shot of the logo lasts a bit too long and starts to glitch...the camera pulls back to reveal the background of the Internet from Our War Game! all in complete silence. Then you hear Diaboromon giggle. Unnerving stuff.
The villains have to be some of the scariest and horrifying villains in anime history. Lets study them in finer details.
Devimon, a cunning, devil-like monster who's the power to brainwash friendly and peaceful digimon into rampaging, savaging berserkers.
Etemon, a super-strong killer monkey whose joval and hammy personality simply hides a psychotic and megalomaniac narcissist.
Myotismon, a mass-murdering, sadistic, abusive, unstoppable psychopath of a vampire who puts even Alucard to shame.
The Dark Masters, a group of powerhungry tyrants who have reduced the Digital World into a dark and lifeless place, kills and destroys everything and everyone around them, enemies, innocents and minions alike, For the Evulz and plans to Kill All Humans in the original Japanese version.
Metalseadramon, a long, violent, hot-tempered, warmongering dragon-like eel clad in golden and spiky armor who, unlike his allies, prefer to reduce his enemies into firing ashes instead of playing games with them.
Puppetmon, a Psychopathic Man Child who seems to think he can make friends by killing and enslaving everyone around him, who kills indiscriminately and loves to play sadistic games with his enemies.
Machinedramon, a cold-hearted, brutal and gigantic Killer Robot who speaks, though rarely, with a growling, hateful and metallic voice and mostly acts like a lifeless machine, unless when he's on a murder rampage, which's when his true sociopathic nature is shown.
Piedmon, who basically is both The Joker and Kefka put together in one extremly powerful and sadistic abomination of a digimon.
Diaboromon, a living, sentient computer virus who looks like a demonic grasshopper, who plans to consume all of Internet, has the ability to clone himself into an army, and tries to nuke Tokyo just to get rid of a few Digidestined. When that fails, he pulls a Godzilla years later and tries to stomp Tokyo into nothing, while renaming himself Armageddemon.