- The execution scene in the first episode. Doesn't help we can see the doomed man's tears soaking through his hood. The crowd shouting "KILL! KILL! KILL!" is also distressing, as their outrage at an unrepentant murderer being released wasn't enough to stop their bloodlust.
- At the end of episode 15, the Count sends Albert back to Earth and then he cries, knowing what he had done to Albert. But when they show close-ups of his face, only half of it is sad, the other half is the evil Gankutsuou smile. Now that by itself is creepy, but when the Gankutsuou side takes over, the cries immediately transform into the freakiest evil laugh ever heard. Joji Nakata provides a knock-out performance and the animation supports the moment brilliantly.
- Andrea Cavalcanti at first seems like an effortlessly charming Bishōnen but is eventually revealed to be outright deranged to the point of seducing his mother and almost raping (or does he really?) his half sister and stabbing his father. And let's not forget Danglar's Death by Materialism, preceded by a good amount of madness.
- When Vilefort begins to go insane from the toxin Andrea injected him with. We get to see it, from his perspective, as his grip on reality comes totally undone, and the once normal classical music that was playing from his stereo becomes a nightmarish wail. The worst part? The scene cuts off before his descent is complete, leaving the rest to the viewers imagination.
- From what little we see of the Chateau d'If, the punishments are horrific beyond imagination. Our only example, the Count, was used as part of the Wetware CPU for its defense systems. The agony was such he actually would have died purely from the pain alone had the same system not been forcibly keeping him alive. Prisoners were only allowed into their cells to sleep for a bit before being hooked right back up, over and over until they finally expire.
- Everything that involves Gankutsuou, especially Albert's nightmares. The execution scene (especially in the manga... ohmygod).
- From Albert's point of view, the whole series was a never ending nightmare. Your mentor and substitute father stalking you and trying to kill you. Your dad turning out to be a parvenu and an opportunistic betrayer and murderer, then trying to kill you along with your mom, then trying to kill a young girl whose father he already murdered.
- Andrea at one point attacks Haydee with a crazy look on his face and looked like he was gonna try to rape her but the Count shows up and he stops.
- The chaos in Paris after Albert's father starts a coup. They leave Parliament more or less unharmed but the same cannot be said of the civilians. In addition to the already terrifying-from-a-civilians-perspective Longsword Mecha, other mechanical monstrosities are seen prowling the streets, killing any who resist (and even some who don't)
- As mentioned above, after Franz's death, Albert has a dream that ends in him killing Franz himself. But unlike in real life where he was stabbed in the dream he doesn't just die; his entire body turns in a mass of blood, as does everything around him and Albert. Talk about a bad dream.
- The end of episode 19 where Andrea assaults Eugenie pinning her to the ground with the intent to rape, ripping her clothes off violently all the while laughing maniacally about how he will "ruin her". It's very distressing to watch.
Nightmare Fuel / Gankutsuou
For an alternate take on The Count of Monte Cristo, Gankutsuou has a few moments of pure Nightmare Fuel. Spoilers below.