The general feeling of trying to escape from a large mob when you're outnumbered.
Any time Nocturne uses Paranoia. It basically removes your vision of friendly champions. This is usually followed up by Nocturne flying across the map to murder someone, and you won't know who until he latches onto his target. To make matters worse, it is implied that it is a spell that affects the summoners themselves, making them mistrustful towards each other for a short moment. And if that wasn't bad enough, it is revealed in the "A Twist of Fate"-cinematic that the champions affected by it also get to see some rather damn creepy stuff similar to that of Dante's Inferno.
Gangplank's laugh when he fires his ult.
Fiddlesticks. Fucking Fiddlesticks. His Ult. is perhaps the scariest as well as the most dangerous. Made worse is that a good Fiddlesticks player WILL do it when everyone least expects it.
The huge-ass Shark that Fizz summons is quite scary the first time. Doesn't help that it's a huge Game Breaker.
If the shark finishes off a small champion, it eats them, as in, it takes the whole body and doesn't leave behind a corpse.
That moment in midair after a Singed fling/Blitz grab as you travel towards the enemy team.
Skarner's ult is the worst with it- before the bug was fixed, teleport used to be considered a debuff. So Skarners would hide in the bush, ult you, use teleport, then hit cleanse to reach their base instantly, taking you for the ride.
Cho'Gath's feast ability. He EATS YOU.ALIVE.
Cho'gath claims to have far worse things in store for you than merely eating you.
DEATH, is NOT the end for you. I have seen to it. For eternity; YOU. ARE. MINE.
Any character that turns invisible is this and Paranoia Fuel. Especially the Joker Expy Shaco with his boxes, and Twitch with his creepy laugh and devastating ult.
Being taunted by Galio, Rammus, and Shen when you least want it.
When you're losing a match and your jungle is unwarded, suddenly the entire map is a very large, empty place, with the entire enemy team hidden just ahead in the fog of war. In every direction.
Warwick, especially when he smells you when your health is low. Just when you think you're safe.....SUPPRESSION!
Any time there's a skilled Rengar on the opposing team. That bush you're running by? He could be in there, waiting to pounce and take your head for his collection. Similar case with Kha'Zix except he doesn't even need a bush - and he'll likely leave less than a head behind.
Cassiopeia's ultimate ability, which petrifies nearby enemies that are her facing her, and to top it off it's accompanied by an almost demonic shrieking sound.
Zac. Oh, sure, he's a nice, friendly blob monster who is actually one of the straight-up good guys among the champion roster. He's also capable of coming from literally anywhere when he initiates ganks. With careful movement, he can avoid the common ward spots on the map, thereby likely bypassing your vision, and then come flying at you from odd angles. While he's far from the only champ with a wall bypass, nobody can bypass walls with the same distance and frequency as Zac. The entire game, you're left wondering if, when, and from where he's going to come at you.
Annie turning her teddy bear into a giant flaming monster. You're chasing Annie, you think you're a safe distance away, and then suddenly GIANT FLAMING BEAR OUT OF NOWHERE, which is likely to stun you while it wails on you with its fiery paws.
"Oh, you're gonna B while low on health? Here, Let me play the song of my people" - every Twisted Fate/Pantheon ulting an unfortunate sap that's low on health.
Similarly, any AD Carry with a Global ultimate. Low on health? "Wanna recall back to base? Here, have a rocket/crystal arrow/glimmering wave in your face!" What makes it even scarier is the fact that, unlike Pantheon's and Twisted Fate's ultimates, you have literally no idea when and where you can expect these.
Karthus's ult is similar. Just escaping from a fight with little health, starting to base, then seeing the green light above your head, signifying that you will die.
The music that plays when you are dead in the Howling Abyss.
Warwick was originally a deranged Mad Scientist prior to his transformation. The fact that someone only became worse when they had been cursed is really saying something. Just how horrible was he prior to his transformation?
Judging by what we saw in Karma's League Judgment, he was an absolutely disgusting bastard who made Singed look like a saint. Singed is merely callous and uncaring; Warwick went out of his way to be as horrible as he could out of sheer sadistic joy in the carnage he was causing.
With the new lore for Warwick, he's even worse. He befriended Soraka, then hired some guys to attack him so that she'd defend him, losing her divine powers in the process. Why? So he could eat her heart.
Singed, Warwick's student. Remember what happened in Riven's backstory? During a war with the Noxians and Ionians, Singed fired off salvos of an extremely powerful chemical weapon with no regard for who he hit, leaving the poor girl shattered mentally at the scene.
Turns out Master Yi was also a victim to this asshole. His village, attacked by Noxians, was brought down to ashes by Singed. Yi isolated himself to ensure that, as the last of the Wuju style, it would not die out.
It can be said this champion is responsible for a lot of champions' fucked up lore.
He may have been a source of humorous memes, but Dr. Mundo may have actually been worse than Warwick. He started his sadistic experiments as a child, and only got worse and worse.
He got a medical license when he became an adult and "had been acquitted of thirty-eight separate charges of murder." Imagine having a serial killer as your doctor. Imagine having THIS serial killer as your doctor.
Urgot's fate. You're basically immortal while being horrendously disfigured. He even laments that it sucks in his current position.
And what comes with his disfigured body? Eternal pain. Literal eternal pain. The only thing keeping him going is his near-endless hatred for Demacia, especially Garen. Come to think of it, pretty much every single thing about Urgot is terrifying.
Renekton. He had been around evil people for too long, destroying his mind and making him go crazy.
Summoner Carin: We have entered your mind, Orianna. How did this make you feel?
Orianna:[creepy mechanical giggle] It was fun. I like memories. Don't you?
Fiddlesticks is bad enough in-game. His lore makes him much worse. He had to be sealed into the summoning chamber because they couldn't get rid of him. Everyone who went in was either cut down or driven mad.
Even worse, all anyone knows about his origins is that a summoner attempted an extra-planar summoning. No one knows what happened or where the summoner went; all that's left of the event is Fiddlesticks.
Also, in the forums, many people had asked for more information about Fiddlesticks; his designer said two words, "He waits."
Some champions have to go to extreme lengths, if not divinely blessed, to get their magical powers. Syndra was some ordinary farm girl who was born with enough power to wipe out her village, and managed to raise a huge floating castle with sheer magical willpower alone.
Mordekaiser has been given new lore that paints him in a more horrifying light. A being of pure agony and suffering that predates the Shadow Isles, Mordekaiser is a master of using pain as a weapon and is on a horrifying quest across the land. A story from a young mage in training describes him interrogating her teacher. He said he would die before talking. Mordekaiser promptly kills him and tears out his soul to get the information.
Elise, the Spider Queen. Outside of being a horrifying Spider Creature, her lore is pretty nightmarish. As the leader of a cult worshipping a Spider God, she will occasionally take a pilgrimage of her followers to the Shadow Isles to find a shrine to their god. Once there... She lures them into a cave where a gigantic, undead spider lays in wait, which eats all the followers and gives Elise venom that staves off mortality a little bit longer. The kicker? Elise does this every few weeks.
Evelynn is a total mystery, and the only thing people can gather from her is that she likes to kill. And is very good at it. What makes this very scary is that nobody knows the real reason for why she is in the league, but whatever the reason may be, it's big and she will probably affect everyone with it.
Though if she and Twisted Fate could get along, maybe she's not the worst thing to step into the League.
It gets better. Almost all of them have specific dialogue for when they capture the West or East Altar. The spirits of the East altar beckon them to let loose their powers, and the spirits of the west either hold them in contempt or tries to reason with their better nature. The spirit of the West Altar also implies that Mordekaiser is actively using Hecarim to his own ends.
Cling, clang, go the chains Someone's out to find you Cling, clang, oh the chains The Warden's right behind you Quick now, the seeking chains Approach with their shrill scrape Don't stop, flee the chains Your last chance to escape Drag the chains, drag the chains With all the strength you may Drag the chains, drag the chains Or they'll drag you away Cling, clang, go the chains There's no more time for fear Cling, clang, oh the chains The last sound that you'llhear.
It doesn't(?) help that he was horrifying both in life and after, as Thresh. In life he was a sadistic jailer. After death, he only got worse - now he tortures you and then imprisons you in his lantern to be taken to a forsaken ghost-hell-island.
Kog'Maw is an Eldritch Abomination who wants to consume everything. One of his taunts? "Terror coming... Daddy coming!"
Keep in mind, someone once witnessed what Kog'Maw does when he is hungry and was both awestruck and chilled by what he saw, claiming "If that's just hungry, I don't want to see angry." Who was the person? Tryndamere.
Word of God stated that Kog'Maw is still an infant, which makes the above taunt of him so much worse. If he is a child, what kind of Eldritch Abomination is his "Daddy"? Whatever it is, you sure as hell don't want to be near the League when he arrives.
Many backstories tie to The Void. Not much is known about the place, which only makes things worse. It must be a rough area if its residents include Kog'Maw, Cho'Gath and Kha'Zix. Not to mention both Malzahar and Kassadin beheld visions of the Void entering Valoran and were forever changed by what they saw. Malzahar was driven completely insane and Kassadin had a part of himself die when he let the Void inside to survive the visions, and both are two of the most dangerous mages in the League (although Kassadin's part was lessened that he still resolved to become one of the most heroic characters in Runeterra and trying to protect its citizens from these terrors that he gained power from).
The latest abomination to enter Valoran, Vel'Koz, may well be the most terrifying of all. A multi-tentacled creature obsessed with the pursuit of knowledge, Vel'Koz is effectively an Eldritch AbominationMad Scientist which studies other life forms through deconstruction. And just in case that doesn't scare you compared to the man-eating monstrosities like Cho'Gath and Kog'Maw, just watch his debut video, "First Contact"...
Vilemaw, a spider which makes Elise seem tiny, and Elise herself is tall and slender. Speaking of Elise, she worships the creature because drinking the venom it produces keeps her from aging for a time. Effectively, Elise is immortal so long as she keeps drinking the venom periodically. Elise can gather the venom after she lures a group of followers to Vilemaw's lair, where the beast eats them alive. And it's not confirmed but we can rather safely assume that Vilemaw is immortal for two reasons: it naturally produces anti-aging venom and is referred to as "the spider god" both in lore and by the game developers. Added bonus: you can see a Dragon/Drake skull in Vilemaw's webbing. Yep, a giant, likely immortal, venomous, dragon-killing spider deity.
Baron Nashor. Killing a Dragon/Drake is heralded as a big achievement by warriors throughout the land and is something that can be boasted about for life. Baron is far worse than the notable Rift dragon. Even Vilemaw can't match his damage or durability. Baron is a large wurm capable of devouring Annie's Tibbers in a single gulp. It usually takes an entire team to take down Baron, and occasionally a person may be able to solo it with difficulty. But what we see in the Rift is actually an incomplete version of what is known of the Baron based on myths and supposed eyewitnesses. Yes, the tough creature is even stronger out of the Rift and it's somewhere by the Serpentine River. Noxus and Demacia will fight each other in many places but both sides make sure to stay away from the Serpentine River. This thing has armies afraid of it.