This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Digimon X-Evolution
The X-Antibody in its own right is not so bad. What's worse is the Death-X-Antibody. If you have seen a Doru-Greymon, you do not want to see a Death-X-Doru-Greymon. It's essentially the same, only darker, more diabolic and with claws that can pretty much rip anything apart.
X-Evolution has the probably most evil Digimon ever shown: Death-X-Mon (or Dexmon, depending on translation). It isn't so bad that it looks like a mechanical dragon, combined with a demon of some sort. It is immortal as long as the main character, Dorumon, is alive. The solution: Dorumon, Digivolved into Alphamon, summons the Ouryuuken (Ultimate Warblade Dragon King Sword, in itself another digimon but that bit isn't mentioned in the film) and throws it like a boomerang, so it hits himself, Death-X-Mon and Yggdrasil, which is the only thing keeping the world from being destroyed.
Somewhat better, somewhat worse: Afterwards, Omegamon takes Dorumon's Digicore and becomes Omegamon-X, and uses a brand new technique, called "ALL DELETE!", which finishes off Yggdrasil leading to the reboot of the Digital World.
The Royal Knights (the good guys) work for Yggdrasil (the deity) who created Death-X-Digimon, including the Death-X-mon mentioned above (The Dragon). And at first they never question a command.
Any battle involving Omegamon. His destructive power is far above anyone else's. In one scene, he managed to curb stomp MetalGarurumon-X and WarGreymon-X, following that with killing Dukemon note that Dukemon let himself be impaled, because "There was something I wanted to check". And that's despite Dukemon being on Omegamon's side.
The opening scene. We get to see Leomon dying in front of Dorumon... and this scene is shown again and again whether it's necessary or not.
Most of all, the deaths of the surviving digimon. Ways to die include death by virus (collapsing and dissolving), disintegration by energy beam, impaling, literally crushing the skull, being ripped to shreds and eaten alive, to list the most memorable ones. All shown onscreen, while the last two where preceded by the endless bloodthirsty cries of the swarm of Death-X-DoruGreymon. That probably had to do with why the film was never dubbed.