Final Fantasy/Nightmare Fuel

Somewhere along the line, Final Fantasy went from a series about knights battling dragons with the occasional surprise encounter and scary monster sprite, to some seriously screwed-up crazy stuff.

Various Games

There are two trademark monsters of the Final Fantasy series that are very creepy, Tonberries and Malboros.
- Tonberries are genuinely unnerving hooded goblin-like monsters with typically enormous health, that would slowly stalk the characters with an oversized butcher's knife until it got close enough to immediately deliver a one-hit kill, while Malboros are hideous and monstrous masses of tentacles and eyeballs with enormous gaping mouths that would either breathe a horrible gas attack that would more often than not wipe out an entire team with status effects or would simply devour and digest characters whole.
- Final Fantasy Crystal Chronicles provides a bit of Nightmare Retardant for the former group. Tonberry Chefs appear as enemies in Moschet Manor, and are identical in appearance to normal Tonberries - except they wear adorable little chef outfits.
- Malboros Also very frequently had "sneak attack" as a base ability, getting first strike on your party in at LEAST one game (very definitely Final Fantasy X). Based on the SIZE of these things one can only wonder how the party NEVER sees them coming...random encounter or not.
- Also, Almost as if answering the previous situation, In Final Fantasy X-2, there is a cut scene where the party is having a bit of a chat with one of the antagonists and as the bad guy(s) start to walk away the camera pans to reveal a malboro STANDING ON THE WALL just above where the camera had previously shown prior to that. Then, to make things worse forever, The malboro is shown to..."slither" down the wall and initiate a battle with the party at such a speed it leaves behind afterimages as it moves.
- Throw in a note of Body Horror with in FFXII the notes on King Malboros say they were once human, but transformed into that lovely visage after putting on the former Malboro's cursed crown.
- Tactics Malboros have a beastmaster technique called Malboro Spores. The effect: Turn a unit permanently into a malboro. One generic unit lampshades how horrifying it is.
- The worst thing about Malboros is with each Final Fantasy game, these things just get more and more realistically rendered. Think those teeth were bad with polygons on FFVII? Just check out this picture of a Malboro from Final Fantasy XIV.
- The worst thing about Tonberries is that they are adorable. If they looked scary, it would be one thing, but you have a cute, squat little critter pacing amiably back and forth across the battlefield, seemingly unconcerned by anything, and somehow that just makes it ten times worse.
- No, the worst thing about Tonberries is trying to figure out what attacks like "Karma" and "Everyone's Grudge" mean in-universe. And it gets even worse in the games where they get some sort of dialogue. "So long have I hated. Hated you, hated them, hated till I grew weary of hating . . . Once more, I pick up my knife. I'm coming for you."
- At the risk of turning this into an unintentional Overly Long Gag: no, the worst thing about Tonberries is a combination of Nothing Is Scarier and the Implacable Man. Given the nature of the Tonberries' attacks, it's reasonable to interpret them as angels (or demons) whose sole purpose is to avenge the wrongful deaths of their fellow "monsters." And they do it all without resorting to a One-Winged Angel transformation or an attack of which You Cannot Grasp the True Form - just a knife, and a long, slow, Unflinching Walk across the battlefield. So far from the lack of over-the-top theatrics diminishing the Tonberries' frightfulness (let alone making them adorable), it serves only to heighten their menace by way of contrast with the rest of the monsters.

Final Fantasy I / II / III

From one of the bonus dungeons in Final Fantasy Dawn Of Souls, you find yourself in a dark as night city, populated by a bunch of zombies that do not attack you—instead, they're exactly like NPCs like you'd see in any other town, only they move half the normal speed, they have greyish skin, and apparently they're in incredible amounts of pain, given what they say when you talk to them (the only thing my subconscious is letting me remember right now is a woman that says "Why... is this happening... to us? We did... nothing wrong..."). Some of the town's people, meanwhile, have been turned to stone (and after they're turned back to normal, they tell you that they were aware of what was happening), and a soldier next to the door to the boss begs you to go in and save them, saying, "Do it...it's the only way..." Oh, and did I mention that the Game Over music is being played the entire time?!
- In that same bonus dungeon, there's another level in which you apparently lay siege on and defeat the inhabitants of a castle. The worst part is, based on their dialogue, you're killing innocent, dying people.
The first one's plot can be this if you think about it. Garland betrays Corneria and captures the Princess, but being an old knight, he's quickly beaten. He's so outraged by this, that he's sent back in time to become the demon Chaos. He then sends the Four Fiends forward in time to make sure the cycle continues. Now, as an immensely powerful demon, he can (and apparently does) kill the Light Warriors. That's how much he hates them. He wants to spend eternity killing them, over and over.
Yoshitaka Amano's monster designs tend to be quite disturbing at best, especially the ones in Final Fantasy II.

Final Fantasy XI

In Final Fantasy XI, Dynamis is a dreamworld that has been corrupted by various dreamers (such as the deceased Shadow Lord). The scary part? The people and beastmen trapped there are stuck in a cycle where they fight each other in vain and death does nothing permanent. One article on the official website shows one of the Hydra Corps member's descent into insanity as he writes to his loved one.
The Pandemonium Warden, whose legendary 18 HOUR FIGHT TERRIFIED EVERY SINGLE PLAYER FOR MONTHS. And It's a voodoo skeleton ambomination. Sweet dreams.
And the Promyvion, or emptiness, levels. They are creepy as hell and the bosses and music doesn't make you feel any better.
Running through a zone without a chocobo, or any way to keep yourself safe when its dark, rainy, and undead and beastmen are all over the place and would happily tear you to peices.

Dissidia: Final Fantasy

Despite Cloud of Darkness being remade into a Sexy Villainess, she's still quite creepy. She always refers to herself as "we," those snakes of hers have minds of their own, when she wins, she swims through the air like a snake, she's apparently "not really a woman," and just in general she gives off a disturbing aura that all of the characters pick up on automatically.
Exdeath. Despite his memetic status, his perfectly executed Ex Burst shows why you don't fuck with him unless you're one of the other twenty-one characters, and even then you'd have trouble. All else fails, he'll simply throw you into the void and crush the entrance as if it were a wad of paper. Said "perfectly executed Ex Burst" involving Exdeath crushing a black hole within his hands (during a slow close-up, people!) is already bad enough, but there's more. While the attack ends with Exdeath crushing the black hole, the music fades out and the screen fades to black. Exdeath's horrifyingly deep "Embrace the stillness of eternity." doesn't help at all, but it gets kinda nasty if you use it to finish a match, since the first thing you hear afterwards is your opponent's death scream without any BGM (as your opponent's defeat - between match and fanfare - hasn't any). Now try defeating Terra with headphones and your eyes closed! There ya go.
- His EX Mode quote: "The laws of the universe mean nothing!" He is altering reality itself to kill you.
And then there's obviously the game's take on Kefka Palazzo.
- Not that he was a nice fella to begin with, but damn. As seen in this video, Kefka chases Terra gleefully and casually casting bolts of Ultima spells everywhere, wrecking his place in the process. His sudden, out-of-nowhere close-ups (like these ones), mixed with his hamminess, make him one of the most terrifying characters in the franchise.
- Mostly, it's shown that Kefka destroys, kills and wreaks havoc For the Evulz, but his EX Burst offers another view - When Kefka executes his EX Burst perfectly, it sounds like he cries "IT'S TURNING ME ON!" in a high-pitched voice, blasts the opponent with his death ray, then whispers in a low voice "That was titillating." Given the tone of voice and the quotes, it seems Kefka doesn't just have fun destroying things, he finds it arousing! Killing people turns him on! Suddenly every single Kefka fight you've ever seen takes on a much darker tone when you realize the endless Fridge Horror that is going to spring to mind now.
- And it that doesn't scare you, remember that in the past Kefka was able to mentally control Terra, who he considers "destruction incarnate." A reasonably attractive young woman with destructive powers to rival Kefka's own, turns into a Cute Monster Girl, and he can control her thoughts... we'll let you draw your own conclusions about some of the ways Kefka may have put his control over her to use.
From Duodecim, there's Feral Chaos. Take a boss who was scary enough in the first game, essentially turn him into the Balrog from The Lord of the Rings, complete with ear-raping roars and screams, give him an even more broken moveset, and a new EX-Burst that makes Exdeath's look downright tame (you get the same lack-of-BGM at the end, but you also get impaled by the giant swords from Utter Chaos, and after that, you get treated to a victim's-eye-view of Chaos smashing your face in with his free claw), and what do you get? Oh, and the best part is, he's fully playable. Have fun online, kiddos.

Final Fantasy Tactics

Moogle Jugglers have the Monster Clown thing going for them. Imagine the Moogle Juggler sub Thief from an in game perspective. 4 Monster Clown Moogles "Smile" chain across the map Till they stand surrounding you. Then they take turns like little fuzzy piranhas "Steal"ing all your equipment (minus shoes) in the first turn, then they proceed to tear the very techniques from your brain in the second.
The animation for the doom and death spells has taken a turn for the traumatizing. In Final Fantasy Tactics Advance, the animation would involve a spooky but cartoony-looking Grim Reaper to come and attack them. In the second game? The character's soul would rise out of their body and 3D inky black spectres with real looking skulls would sweep in from the bottom of the screen while saying "I'll be taking this." ("this" being your immortal soul). And they just have really creepy voices. How do Phoenix Downs even heal THAT?
Is that...Is that a dismembered naked woman...WHO'S STILL ALIVE??? That's Zalera. The woman he's holding is a shamaness he took hostage to keep the gods from punishing him (it didn't work). He uses her dying screams to power his magic. Where do you learn this? In Final Fantasy XII, where you fight him.
The Lucavi in the original. When one of the bad guys pulls out the stone, there's a lovely little sparkle to show it's a beautiful gem before a blinding light of one color or another shimmers around the boss, with screaming souls being sucked into the vortex of agony that transforms normal men into horrid abominations. Then another explosion shortly after ejects these souls to expose the demon you must now face. Chulainn especially. At first he's a big bag of fat flesh that kinda looks like Oogie Boogie from The Nightmare Before Christmas, which isn't so bad. But then he opens up his belly and reveals that he has a giant mouth with teeth in there! Oh dear lord!
There is also the Massacre at Riovannes. Oh, good lord, the blood. The near dead kid Isilud, squashed heads, ripped apart bodies, and then Wiegraf goes Omnicidal Maniac...of course, it's not really Wiegraf, but instead a That One Boss of epic proportions. And the whole place is being futilely guarded from the outside. Imagine you and your brother are guards. You actually live and retreat, and go back inside the castle...only to find your brother without much for a head...
While it is most certainly delving into fan theories more than what the game itself details, Delita is the epitome of a monster, despite being called the Hero of the Lion War. Consider that aside from his numerous murders and executions, the fact that he used and eventually murdered Ovelia. Then there is the theory that some people enjoy where in he finds Balmafula spying on him, so he proceeds to rape her and cut out her tongue. Nothing quite like that first year of rulership, huh?

Final Fantasy Crystal Chronicles

The premise of this is very disturbing, especially after playing Ring Of Fates, which is a prequel. Essentially, it's a Crap Saccharine World set After the End - most people are dead, people have to live in little villages protected by Myrrh (Phlebotinum) which they have to collect from trees every year. There are miasma streams which need elements on your chalice to get through, and miasma everywhere not protected by myrrh. And then there's the village which was destroyed when its caravan didn't come back, instead the people dying and being turned into undead. Since you have 'memories', I'm assuming an Amnesia Plot later in the game.
- Oh that's the half of it. There's the chilling story of a young man from your hometown of Tipa who went off in search of a way to rid the world of miasma. He never returned. This young man is Hurdy and Gurdy who, after meeting with the mad, memory eating god, Raem, had his memories stripped away and developed a split personality, the priest and the swindler. He also had a bodyguard, a Lilty named Leon Esla from Alfitaria. You may be familiar with his son, also named Leon Esla, whose father was killed by the Black Knight. He met a similar fate, without his memories he went insane and spent the rest of his days chasing a "light" that only he can see, assuming that it took his memories. In the end, his son kills him for revenge. In his dying moments, he regains his memories but it is too late. His son never knows that the Black Knight was actually his father but his wife, present at his death, realizes it.

Agni's Philosophy Final Fantasy

The trailer is essentialy 4 minutes of "What the FUCK SE!" If you thought Versus and Type-0 looked dark...