This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Resident Evil: The Darkside Chronicles
The training facility from Code: Veronica is depicted here covered with Alfred Ashford's insane graffiti and littered with boobytrapped targets used by the unlucky trainees.
Chief Irons's death in this game is arguably more terrifying than in Resident Evil 2. Whereas in that game, the G Embryo carved its way out through one half of his body, in this game it seemingly fused with his skeleton and muscles as it breaks out from him and leaves behind his skin like it was some suit.
The Chief himself wasn't much better, going from debatably stuffing the Mayor's daughter to outright doing it.
The two "Alfred and Alexia" voice files, which at first appear to be them congratulating some girl named "Tanya". Then it sinks in that Tanya was some poor innocent girl who had the misfortune to be a child prodigy the same age as Alexia Ashford and possibly just as smart, which caused the jealous Enfant Terrible to use her as part of her experiments. Her decision to use cryogenic suspension to find a way to "coexist" with her T-Veronica Virus? That came about as a result of the experiments she performed on Tanya.
To make it all the more creepy, it's very likely that the two people on that voice file was just Alfred all along, judging by the fact that during that time, Alexia was still in stasis and the Alexia we hear in said files is using the deeper, more mature tone that Alfred uses when he's posing as Alexia. It could have easily just been his mad delusions.
The three voices files featuring Annette and Sherry Birkin. They are just simply full to the brim with every parent's nightmare; a situation where they are unable to be there for their children and are fearing for the child's life. Annette's situation is a hundred times worse. Not only is her husband indirectly responsible for the G/T-Virus outbreak in Raccoon City, but she's busy attempting to fix the mess all whilst only able to keep in touch with Sherry via telephone; calling to get Sherry excused from school and running home to grab something and then to the police station, Sherry all on her lonesome in the midst of a starting Zombie Apocalypse. The last few seconds of the third audio file are heart-pounding terrifying as Annette is now fully aware that this "monster" Sherry just heard is what once was her husband/Sherry's father, and now it's after her....
The returning monsters have been given redesigns, ranging from a slight cleanup to a complete overhaul. William Birkin in particular is downright horrifying.
Special mention goes to Mutant Steve's redesign. In Code: Veronica, he looks downright funny, because it looks like his head was pasted on a monster body and turned green, while the fangs are only noticable in a close up and the eyes aren't creepy. Now, he's got a permanent grimace that shows off his fangs constantly and the overall nature of the mutation is even worse because the player can tell that it's Steve, but it's incorporated into his monster form well enough that it's not funny, but disturbing. And his mutation is also worse, with his skin bubbling like Curtis Miller's G-Mutation and his voice acting being more convincing.
Steve has a serial number on his arm. In the same place that concentration camp victims had their serial numbers. Let that sink in.
The means Javier took to help Manuela overcome the effects of the Veronica virus; kidnapping girls about her age, killing them, and transplanting their organs into Manuela regularly to keep the virus at bay.
The hidden passageway in the second to last level, which is covered in what appears to be walls of blood, cobwebs and guts with skeletons littered throughout the room. This room is where all of Javier's victims were possibly killed. There are also two Plague Crawlers in here, which are essentially giant cockroaches that hunt for human flesh.
Alfred Ashford. On the way to Alfred's 'training center', you see insane, demented graffiti on the walls showing people dying bloodily, a family drawing with his father scribbled over in red, and images of a boy and girl saying 'hello' and 'goodbye'. And this isn't normal graffiti, mind you. It's all drawn as if it was done by a small child. The elevator ride down reveals a door surrounded by drawings of eyes and the word 'die' scribbled so many times over the door it's almost illegible. And then you get to the actual 'training center' ... which is called a 'Kill House' filled with targets, zombies, and more insane graffiti. Yeah. Frankly, you'd rather face an entire island of monsters than deal with a guy this insane.
That giant freaky doll inside their mansion is even worse in this version.
And the title of the background music for this part on the soundtrack? Insanity's Palace.
The redesign of Steve as a monster. It's creepy. The way his face is incorporated into the monster form is gaunt, fanged, in a perpetual scowl, and somehow melancholy, like Jill in Resident Evil 5. It gives that impression that he knows what he's doing and can't stop himself from following Alexia's orders. And how he mutates. His skin bubbles. It's not a smooth change. It looks like it hurts. A lot.
The actual design of Monster Steve's body has changed very little (they gave him a semi-exposed heart... and that's about it). It makes more of an impact because it's being rendered with much better graphics. The Nightmare Face, however, is new, and it makes all the difference in the world, along with the relatively small detail of his neck, namely that in order to bring his head up to look at you, the neck was made visibly longer than the human norm, and is twisted at a somehow disturbing angle.
The ending, where Wesker speculates that the mutations are based on emotions, which are linked to the various chemicals in our minds. Think about this for a second.
The first appearance of G-Birkin in this take on RE2. You, Claire, and Ada are going to find Ben and are going through the door in the underground parking lot. Then you hear Ben screaming as something kills him, and the thing that killed him slowly comes towards you, forcing you to hide. Then when you investigate, you find that Ben was lifted superhumanly high as indicated by the big trail of blood on the wall. And when you go into the room with the plug door, he ambushes you out of nowhere. Oh, and he still has the bullet wounds from where he was shot repeatedly. Fun!