It's an Underfell interpretation, it's bound to get dark at numerous points.
- The "gameplay" starts out normally until the human first interacts with Flowey, causing the screen to briefly glitch out before the Flowey seen suddenly appears extremely battered and miserable, and the song "Your Best Friend" plays in an ominously slowed down and low pitched tune. Flowey hesitantly tells the human that it's "kill or be killed" in the Underground and claims that he'll have to kill them, only for him to crack under the pressure and reveal his true colors as a flower who is scared to death due to how long he's been living in a murderous Underground.
- All of the hostile monsters the human faces, described by Flowey as "malicious" in episode 4, are colored blood red in battle until certain ACTs are fulfilled.
- Toriel's appearance. In the overworld, her eyes are yellow, her sleeves are dirty, and her robes are tattered. And her dialogue portrait is enough to give little kids nightmares. She pretends to be friendly to the human and glares threateningly at Flowey the moment she sees him. Then as soon as she leaves, Flowey tells the human that Toriel murders everything she sees and loves killing humans.
- Ever wanted to know what happened if Napstablook was terrifying? Well, you may not like the answer. The encounter with him is the same as normal, but this time he seems to be genuinely asleep. However, once we try to move him by force, he transforms from a Bedsheet Ghost to a Ghastly Ghost. With his white form turning black with a red highlight, and has now opened his luminous red eyes. And then it goes From Bad to Worse once the battle with him starts. His battle theme, "Ghost Fight", has been so heavily slowed and distorted, that is sounds completely melancholic. And then we get a better look at his Nightmare Face, which now has a Ghostly Gape that is also glowing red. And the creepiest thing about him is that red Ectoplasm is constantly leaking from his hollow eyes and grinning mouth. And of course, his Berserker Tears are red as well to further invoke the appearance of blood. And while he is still one of the easiest mini-bosses, he has a face that is hard to forget.
- Inside Toriel's house, there is blood and dust everywhere, as well as some broken furniture. What ever happened in there, it was definitely some kind of struggle.
- Toriel kept the remains of a human she killed in a bedroom and never bothered to clean it up, so when the human and Flowey walked in, they saw blood everywhere, decaying organs assorted on a table, and a human skeleton with its flesh still rotting off.
- When the human confronts Toriel, her eyes are completely pitch black.
- During the fight, not only does Toriel have more aggressive attacks, but as the human keeps sparing her, her confusion slowly changes to anger and her attacks briefly become more aggressive until she becomes reluctant to fight.
- This AU's interpretation of Sans. Unlike most other interpretations of Underfell, this Sans is much more serious about killing you than his brother. The only reason that you're not immediately dead is because Papyrus has certain standards for killing.
- The "Feraldrakes" found in "Hell's Forest". They are notably different from the other Snowdrakes in the sense that they're constantly drooling and their sclera are black until you pacify them.
