This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Castlevania: Lords of Shadow 2
Soon after he wakes up in the present, a starved-of-blood and half-berserk Dracula is given a meal by his old friend Zobek; it consists of a family of three, including a daughter who couldn't be older than thirteen. After the husband tries in vain to beat Dracula to death with a metal pipe, Dracula slits his throat in a single strike, killing him. He then drinks the mother's blood until she's little more than a desiccated husk, then he turns on the daughter and the screen cuts to black as he lunges for her (did we mention you have to be the one press the O button to make him feed?) When he regains consciousness and looks into the room, the quick expression to cross his face makes it seem as if even Dracula was disturbed by what he did while he was insane from bloodlust.
Once you open the 'fridge,' Dracula himself becomes this when you realize that the technical good guys of the setting, like the Order, have just about no chance of beating him because, if it wasn't enough that he's the most powerful vampire and Lord of Shadow to ever walk the earth, then The Reveal that God STILL favors him as his champion, rendering him almost completely immune to holy weapons and thus making him effectively immortal, makes things that much worse for who anyone who dares face him. Maybe in the grander scheme of things, it's for the best, but it's not so great for the vast majority of ordinary people who lived under constant threat of him during the height of his power. Think about it. A nigh-unstoppable monstrosity who ravaged the land and has consumed countless innocents and with God's total blessing.
The Blood of the Castle is a very disturbing form of corruption that proves that not only is the Castle now a Genius Loci, it's very angry and wants to kill you. Standard fare for possessing something is to wait until they prove their intentions are to help Dracula, then a giant clawed hand shoots out of a pool of blood and drags them downward, and they re-emerge a moment later possessed by the Blood. This is a force with so much hatred in it that even Dracula's servants who have held Undying Loyalty for nigh-on a millennia are turned into his enemies in a matter of seconds. It gets even worse when you fight Inner Dracula.
The worst part? This is Dracula's dark side manifested. This scary factor somehow manages to get even higher, when it starts whispering "I'll always be with you..." Over and over again.
At the end of the game, when Satan is finally summoned from Hell, the first thing he does is slowly and graphically rip Guido's face off. The face is still alive when he throws it aside.
The Revelations DLC adds a whole new area's worth of Nightmare Fuel with the Forbidden Wing. According to Marie, Gabriel shut himself away in here after he trounced the Forgotten One — and lost his mind. Entire rooms are flooded with blood and there are phrases written in it in Latin, scattered all over the floor and walls, which are Dracula's insane ravings and curses of doom upon humanity, the Brotherhood, and Zobek. And it doesn't help that you can hear barely audible screaming and occasional laughter.
Dracula's eyes. Especially when you see them up close and he's mad or angry. The mere fact that they're red doesn't make them scary. The pupils and irises in his eyes dilate and look utterly inhuman. This, in conjunction with the fact that his eyes glow red more or less depending on how enraged the Prince of Darkness is, adds to just how fucking scary they look.
The second Acolyte may be the scariest enemy in the entire LOS trilogy. With his calm, assured demeanor and initially overwhelming power, the only thing you can do is crawl away from him like a whipped dog while he casually stalks after you, zapping your very soul with his force lightning. And what happens if he catches you? He'll open a portal and send you to the pits of Hell. His taunts during your boss fight with him certainly don't help, considering that, as a child of Satan, he knows exactly what he's talking about.
Nergal: Your suffering will make Hell itself cry! Your soul will go mad in eternal agony! Your existence will know only pain! My father eagerly awaits you in his kingdom. Don't make him wait. Perhaps my Lord will allow me to...look after you, once he's tired of your soul.
The part where you have to elude Carmilla as she pursues you in the castle library with a lantern.
Satan's daughter gets in on the promises of a Fate Worse Than Death for our Prince of Darkness, and anyone standing next to him.
Raisa: Ah, my dear Zobek! If only you could see what I see... I see you hanging while my brothers skin you alive! I will bathe in your blood in the presence of my father! The lost souls of the Avernus will welcome you with their cries. Bless me, father. For today I will deliver unto you the Dragon!
During the boss battle with the Necromancer, he summons a bunch of zombies to battle Gabriel. Cripes.
The level where Dracula has to make his way through a maze and elude Agreus is not only annoying as hell, but pretty damn scary as well, especially when Agreus detects you, swiftly catches up to you, attacks you, and sends you right back where you started, meaning you'll have to go through the maze all over again.
The first time you fight the Riot Police qualifies as a classic example of the Mook Horror Show. Put yourself in one of those men's shoes; you and two of your buddies are tasked with killing civilians that are infected with a demonic virus that is turning your home into a literal Hell on Earth. Before too long, you come across a dark-haired man in a red coat who's apparently immune to the virus, so you ask him to come with you. He politely tells you no. So you decide to bring him in by force, and find out the hard way just who you're dealing with when he starts tearing into you and your mates with a whip that looks like it's made of solid blood, zipping around far faster than any human should be able to, and occasionally swapping out for a glowing sword that saps the life from you and a pair of flaming gauntlets that shoot fireballs that turn your jetpack into a useless lump of metal. Next thing you know, he tears one of your friend's throats open with his mouth and drinks his blood and fries your other friend's skull inside his helmet with those gauntlets. He sends you flying with another blow from that whip and you quickly get back up, already knowing how completely and utterly screwed you are... But he's gone. Maybe he decided to let you live so you could warn the rest of the police to stay away. Suddenly, you feel his hand plunge through your chest from behind, and the last thing you see before you die is your still-beating heart, clutched in his fist.