Steins;Gate 0/Nightmare Fuel

Being Darker and Edgier, Steins;Gate 0 contains not just more of terrifying moments, but the gravity of said moments of heavier, too
 * As he is heading home one night, Okabe has a nightmarish hallucination in which he sees Kurisu explode into a bloody mess, her chilling final words echoing in his mind, and is confronted by her numerous corpses lying in front of him. This whole scene is backed by a distorted version of "Gate of Steiner", adding to the horror. And this is just the first episode!
 * The idea of interacting with an Artificial Intelligence seems harmless on the surface, but what if that same A.I had the physical likeness and voice of the person you loved? That's Okabe's predicament; not helping is that Maho has to constantly remind him that the face and voice on his phone is not the same person he knew. But no matter how many times he has to be reminded, Okabe cannot help but get attached to Amadeus like she is a real person. Top it off, there are times when Okabe has inadvertently without realising it after calling Amadeus. First time this happens, Amadeus tells him that he called her back almost immediately, but the scary part is that Okabe has no recollection of doing so.
 * In Episode 6,, just like in the Alpha world line. No one dies this time, thankfully, but the fact remains that , it doesn't help to put Okabe's mind at ease, even without time travel being in involved, nor with secrets being leaked. After all, there is a reason why Okabe is incredibly paranoid around Moeka, considering she was the one responsible for Mayuri's death in Alpha. The worst part is that no one else knows this feeling, so he can't turn to anyone for consolation (although Suzuha seems to be at least aware of this).
 * At the start of Episode 4, Okabe finds himself in the midst of a war being hunted, only to find out he was having a nightmare...or was he? His Reading Steiner might be giving him a PTSD episode of an event that hasn't even happened yet!
 * At the beginning of Episode 9, we learn that Fubuki, one of Mayuri's cosplay friends, had also collapsed two episodes prior at the exact same time Okabe did. She claims to have to had a dream in she saw Mayuri die repeatedly, and seeing Okabe in said dream; in short, she has memories of the Alpha world line. It is here that Okabe realises that Reading Steiner is not exactly a good thing to have.
 * In the game, she and a bunch of other patients recall having identical dreams in addition to being unable to discern between fantasy and reality. This dream is the same one that Okabe and Fubuki had in which they are in the middle of a war torn Japan. Okabe practically confirms that the symptoms of these dreams are the same as Reading Steiner, meaning that his belief that this power is universal is not only true, but it also means that people are in hospital diagnosed with an illness they don't even have!
 * While in 2000 helping Suzuha to solve the Y2K Problem, Kagari suddenly sees an uncanny face in the sky speaking to her. She suddenly goes blank faced, mutters "I hear the voice..." and points a gun at Suzuha to stop her from changing the future. Yes: a child out of nowhere is threatening someone with a firearm!
 * The end of the Episode 13, in which Okabe and Moeka come across an abandoned facility (well, sort of; from Moeka's observations, it was used recently), which turns out to be the place where Kagari was kept for for around 12 years. As the pair venture deeper into the facility, they find a secret room that has a shit ton of crazed messages scrawled all over the walls and the floor, all along the lines of "I miss you", and "Mama", and so on, so forth. This is another example of Madness Mantra that is no stranger to Steins;Gate, but to make it more horrifying, Okabe realises that Kagari was indeed brainwashed, as he had feared earlier. We knew she was a bit odd when we first see her (as an adult), and the circumstances surrounding her disappearance for most many years after she was separated from Suzuha in 2000 remained a complete mystery. As it turns out, Kagari was never safe from her handlers; no matter what era she was in, she was nothing than a puppet for those who were pulling the strings. But the one thing that remained was her love for Mayuri, whom she missed dearly; so much so that she was practically embedded in her psyche for all this time.
 * The second half of the series gets dark real quick, featuring more bloody violence and injury detail, people getting murdered on screen, and harsher language being used more frequently (no F-bombs being dropped though). Part 2 carries a BBFC 15 rating in the UK because of this.
 * Remember in Episode 1 when Suzuha described how her mother was killed in her time period by a military drone? Well, 14 episodes later, and we get to see this for ourselves. And it is every bit as horrifying as she described! Even with Gory Discretion Shots keeping us from seeing everything, from Suzuha's point of view, watching her mother die horribly like that must've caused extreme psychological and emotional damage!
 * Suzuha's cries of anguish as she holds Yuki's blood-soaked corpse in her arms does not make it any better.
 * The second time Okabe . When he awakens, the first thing he sees is destruction everywhere. No one is around, the streets are barren. Then he is confronted by 2 soldiers demanding his name and ID lest he gets executed. Okabe has no idea what is going on.
 * In the game, was involved in the attack against Okabe, Daru, and Maho to retrieve Kurisu's laptop. When we see her again at the beginning of "Presage and Recognise", she is holed up in her apartment (which is still an absolute tip), battered, bruised, bloodied, and bandaged up from several gunshot wounds. The worst part is that she had gone 5 months without any proper treatment, so her wounds likely would've been infected. Had  not shown up, she probably would've died...alone...again.
 * As much as the act speaks of Okabe's determination, just think about the long, agonising journey he had to take just to get back to . Even when . The mental toll that many time leaps would have must've been ungodly!
 * When Kagari goes full on Berserker Rage, the amount of death she leaves in her wake is unfathomable. The anime is worse because we actually get to see the brutal ways in which she dispatches her enemies.
 * In the final episode, Suzuha and successfully escape into the past, but the time machine is almost out of fuel, forcing them stop off on August 21st 2010 for only one minute to prevent a time paradox from occurring. They do run out of fuel, leaving them drifting through limbo until they land in whatever time period the machine ends up in. Where do they end up? 18,000 BC. No life, no civilisation, nothing. Even though, one must ask how long the girls were stranded in that year for.