->''"I met her on her first night in costume. She seemed genuinely interested in becoming a hero. I suspected she would go that route on her own, so I didn’t push her towards the Wards. I ran into her two more times after that, and the reports from other events match up. She went further and further with each incident. More violent, more ruthless. Every time I saw it or heard about it, I expected her to get scared off, to change directions, she did the opposite. She only plunged in deeper."''
-->-- '''Armsmaster''' on Skitter, ''Literature/{{Worm}}''

A recurring scenario where a character, after committing a small act of evil, finds himself becoming more and more evil, very often far more than he originally planned or intended.

Sometimes you can see what you want just beyond your reach--you don't have to jump off the slope, and it's not all that steep anyway, just a few steps on TheDarkSide and you'll have it. Yet what was just a short walk in one direction is not so easily traveled in reverse. Even if you turn back immediately afterwards, you find yourself slipping down the slope faster than you can climb your way up! Eventually you may tire of fighting it and just let yourself continue to slide unhindered, or even worse: choosing to [[ThenLetMeBeEvil embrace the inevitable]] and turn your steps in the direction of your momentum.

This can be done for different purposes:

* A [[{{AnAesop}} warning]] that doing some evil, no matter how good an idea it seems, is always a bad idea.
* A [[{{AnAesop}} warning]] that once you commit an evil act, no matter how small, you are easier to be tempted or otherwise persuaded to commit more and more evil.

For obvious reasons, almost mandatory in StartOfDarkness stories. See MoralEventHorizon for when someone commits an act so heinous and unforgivable that he is now unquestionably evil, and often marks the end point of this character arc. See also HadToComeToPrisonToBeACrook, which is when one of the reasons for falling is spending time in jail, and ThisIsYourBrainOnEvil, for when performing an evil act is akin to drug intoxication, and thus very likely to provoke this trope. A common way of [[SubvertedTrope subverting]] this is for the character to make a SuddenPrincipledStand, when it becomes clear that the character has found a foothold on the seemingly slippery slope and will sink no further. Do not confuse with JumpingOffTheSlipperySlope, which is when someone on the same side of the heroes but on a morally gray path commits an evil act to prove the rightness of the heroes' path.

Supertrope of HeWhoFightsMonsters, wherein fighting against evil is the thing that causes the person to slip into evil. See also ProtagonistJourneyToVillain. Can coincide with BigBadSlippage.

!! Examples:


[[folder:Anime and Manga]]
* Lelouch and Suzaku in ''Anime/CodeGeass'' become more and more radical during the show's progress, although their goals were noble [[spoiler:and successful.]]
* ''Manga/{{Naruto}}'':
** Sasuke didn't just slide down the slippery slope, he grabbed the sled [[spoiler:Itachi [[NiceJobBreakingItHero stupidly]] gave him]] on the way to the edge so he could get down faster. First, he betrayed the village by joining Orochimaru just so he could get strong enough to kill Itachi. He at least had some qualms about killing at this point. [[spoiler:Later on, after killing Itachi, he learns that Itachi massacred their clan under orders from ''four'' of the higher ups (one of which was against it but overruled) in order to stop a civil war that could develop into a ''world war''. Naturally, Sasuke decides that the ''entire village'' has to die because of this. By the time he reaches Konoha, he is not above cold-blooded murder of even his allies just to accomplish his goals.]]
** And he gets worse! Regardless of his statements of genocide, at first he tried to protect the friends that helped him on his revenge quest. Later, however, he'd gotten to the point that anyone who inconveniences him or his goal must die. [[spoiler:Poor Karin.]]
*** [[spoiler:This is later revealed to be caused by a genetic disorder, which drives members of the Uchiha clan insane.]]
* In ''AudioPlay/SaintBeast'', Zeus' slip starts with overthrowing the old gods, which he feels [[IDidWhatIHadToDo a measure of regret about]], but thanks (in part) to [[DragonWithAnAgenda Lucifer's]] support, by the time Judas suggests purging the evil angels in heaven, Zeus has basically [[SanitySlippage lost it]] and keeps getting worse.

* Winnowilll in ''ComicBook/ElfQuest'' is initially at least reluctant to kill to further her ends. Ironically, her descent into cold-blooded murderess seems to be at least partially due to a botched mind-healing attempt by Leetah.
* Officer Bill Petit in ''ComicBook/BatmanNoMansLand'' is a textbook case of a WellIntentionedExtremist going DrunkWithPower:
** He starts off as a loyal member of Commissioner Gordon's "Blue Boys" trying to maintain order in Gotham, and though he advocates a more ruthless approach to the various psychopaths and criminals they have to deal with, it's hard to argue against him in light of the fact that there's no longer even a CardboardPrison to keep them in, and innocent people are being murdered ''every day'' as the gangs fight for turf.
** Later, while still a member of Gordon's team, he publicly executes one known murderer to convince the other criminals that the Blue Boys aren't kidding when they tell them not to cause trouble. Gordon calls him out for this, but Petit's reasoning is sufficiently sound that they can't really call him a murderer, and they let him stay a member of their team.
** Later, he leaves Gordon's team out of disgust for their maintaining their soft approach to crime even when it's clearly not working, but is justified enough that a large number of the Blue Boys leave with him, and neither Gordon nor Petit consider each other enemies at this point.
** Then, after realising Oracle is an invaluable source of information, he launches an attack on her tower to bring her in alive, but tries to kill Nightwing when he intervenes, prompting Huntress (who had been swayed by his arguments and actually joined him willingly) to intervene, but Petit and Huntress agree to keep working together.
** By the end of his arc, after Batman's return and aid to Gordon has made the Blue Boys more effective, he's become so paranoid about losing face in front of his own men and criminals (he calls it "loss of morale") that he forces all the residents of his territory to attend his "Christmas feast", and won't let them leave without his permission, even when the Joker attacks. Finally, he starts shooting left and right at people he thinks are the Joker, even though his own people are warning him that it's a DisguisedHostageGambit, and then when one of his most loyal subordinates tries to leave to get reinforcements, Petit shoots him on the spot while screaming "No-one leaves without my permission".
* Though he's yet to become ''completely'' evil, a major theme of ''ComicBook/TheWalkingDead'' is how Rick becomes more and more amoral as time goes on and he becomes more desperate. As one reviewer put it, it's like seeing what it would take to make [[Series/TheAndyGriffithShow Andy Griffith]] have a mental breakdown and eat the citizens of Mayberry.

[[folder:Fan Fiction]]
* In ''Manga/DeathNote'' fanfic ''FanFic/{{Fade}}'', L gets his hands on a Death Note, containing a part of the story of Kira's rise to power. Trying to stop that from happening leads to L's own StartOfDarkness as he becomes [[NotSoDifferent more and more similar]]—and arguably worse—than the killer he's trying to find.
* Harry in ''[[FanFic/TheDarknessSeries Harry Potter and the Descent Into Darkness]]'' after he hits the DespairEventHorizon when his "friends" abandon him during the Tri-Wizard tournament and, in order to ensure his survival, he begins studying [[BlackMagic the dark arts]].
* In [[http://tvtropes.org/pmwiki/pmwiki.php/FanFic/TheMasksWeWear The Masks We Wear]], Zuko has no qualms firing off lightning against Appa during the invasion of the Fire Nation.
* In ''Fanfic/XCOMFromTheAshesOfTemples'', Commander Bradford gets hit hard by TheChainsOfCommanding and starts making more and more ruthless decisions in his desperation to keep XCOM running. Even Vahlen calls him out on it.

* Michael Corleone in ''Film/TheGodfather''.
* Creator/ChristopherEccleston's character in ''Film/ShallowGrave''.
* Anakin started to feel doubt and hatred in ''Franchise/StarWars: Film/AttackOfTheClones'', killing an entire population resposible for killing his mother (regardless of individual involvement). If not that, then Sidious manipulating him into killing Dooku probably marks the pivot, [[spoiler:and the children's slaughter the end of the slope]].
* Peter Parker in ''Film/SpiderMan3'' slides very slowly. First, he combs his hair differently, then he refuses to pay his rent to his landlord until his door is fixed, and after that he finally performs evil acts, such as emotionally manipulating his friends and co-workers, punching his love interest (accidentally), [[ArsonMurderAndJaywalking and performing a very awkward jazz number for no obvious reason.]]
* Stephen in ''Film/TheIdesOfMarch'' goes from idealism to cynicism and worse.
* Magneto in ''Film/XMenFirstClass''; a really good and interesting example in that he starts the movie already as an AntiHero and spends most of the movie establishing his attitude that would cause him to slip into evil before he actually does so. And while he's undeniably a {{Jerkass}} in opposition to the heroes by the end of the movie, he still isn't evil and never really crosses the MoralEventHorizon.
** Within 11 years between ''Film/XMenFirstClass'' and ''Film/XMenDaysOfFuturePast'', he became involved with the JFK assassination (while he claims to have been attempting to ''stop'' it) and [[spoiler:launched an attack against the White House.]]
* Discussed in ''Film/TheEliteSquad'' with regards to {{Dirty Cop}}s.
--> The first time is always for a good cause. But once you steal for the force you'll also steal for your family. That's how the system works.
* ''Film/RoboCop2014'':
** Dr. Norton. At the start, he doesn't want anything to do with weaponising his cyborg technology, but Sellars talks him into working on [=RoboCop=]. As the film goes on, he starts making bigger compromises, such as tinkering with Alex's brain and body chemistry, which have the effect of reducing his humanity. [[spoiler:Eventually, however, [[HeelRealization he realizes just how far he's gone]] and seeks to repair the damage.]]
** Sellars himself. He begins the film as a guy who simply wants to sell his machines to the American government, and unlike his counterpart Dick Jones in [[Film/RoboCop1987 the original]], those machines actually work. He slowly toys more and more with Murphy, treating him less as a man and more of a useful product as the plot goes on, and once he utters [[spoiler:"you know what's better than a hero? A dead hero"]], you know there is no turning back.


* In ''Literature/MemorySorrowAndThorn'', this trope in a nutshell is the Backstory of the BigBad, the Sitha prince Ineluki. Once a purely heroic figure, his ambition and willpower darkened when the Sithi's lands were invaded by savage humans. Dismayed by his people's despair in the face of their approaching doom, he delved into Things Man Was Not Meant To Know and constructed a weapon so terrible that his father, the king, insisted he destroy it. Maddened by this rejection and by his torments, Ineluki murdered his father and took the crown, leading a final, futile resistance against the humans that ended in his death via DangerousForbiddenTechnique. He is at the start of the story the BigBad and an OmnicidalManiac.
* Conall Haldane in the ''{{Literature/Deryni}}'' novels ''The King's Justice'' and ''The Quest for Saint Camber'' goes from merely being a RoyalBrat and SoreLoser to committing murder and treason. He says as much at his trial: "I didn't start out to betray you, Kelson," he sobbed, "but things -- happened. It wasn't fair!"
* This is the big reason why the Laws of Magic exist, and why the Wardens exist to enforce them in ''Literature/TheDresdenFiles.'' The [[BlackMagic types of magic prohibited by the Laws]] all lead the caster to want to use them more often, eventually turning him into a villain. The Wardens will sometimes grant clemency on the first offense if it can be proven that the offender didn't know any better ''and'' a senior wizard offers an apprenticeship to oversee the offender's redemption. In any other case, summary execution is prescribed.
** Also, this is a major fear of Harry's after [[spoiler:taking up the mantle of the Winter Knight, more so after he finds out that this basically dooms him to becoming a monster.]]
** [[TabletopGame/TheDresdenFiles The roleplaying game]] reflects this by giving Lawbreakers mandatory stunts that cost them refresh whether they like it or not but [[ItGetsEasier provide them with bonuses towards breaking the same laws again]]. Of course, they technically never ''have'' to use those bonuses (which come with additional drawbacks if one keeps taking advantage of them anyway, literally changing who the character is over time as he or she gets twisted by the ongoing practice of forbidden magic), but once things get desperate and the temptation great enough...?
* A major fear for the kids in ''Literature/{{Animorphs}}''.
--> '''Rachel:''' ''[narrating]'' "I know it's wrong," he said. "But it doesn't matter. We have to do it. It's a war. We have to win." I had to laugh. People sometimes think that I'm a bad person, a violent person. But even I know that the words "we have to win" are the first four steps down the road to hell.
* In the Literature/SherlockHolmes story "The Man with the Twisted Lip", the resolution is that a respectable journalist first poses as a beggar for the sake of research, then discovers this pays way more than his job (if done artistically enough), then uses begging to get out of a medical debt, and finally abandons journalism altogether, becoming a professional beggar.
* ''Gingema's Daughter'', the first book in Sergey Sukhinov's ''Emerald City'' series, is about the adventures of Corina, originally an ordinary, if somewhat lazy, girl. She starts her way as understudy of Gingema, then runs away to travel with her wolf companion. She lives by different families, usually helping them magically in secret. But gradually, she decides that BeingGoodSucks, since everybody bothers you with requests, and being feared is as important as being loved. She deceives the Woodsman to do her bidding by pretending to be the daughter of his former sweetheart, and ultimately manipulates him into deposing the Scarecrow, thus becoming the ruler of Emerald City. The rulership she establishes is a CrapsaccharineWorld: there is food for free and low taxes, but do cross Corina in any way and you are dead or turned into a small animal. By the second book, she kills Ellie's parents and becomes a fully-fledged villain.
* Made explicit in CS Lewis's ''Literature/TheScrewtapeLetters'', which is a satirical exploration of Christian theology, detailing a senior demon's advice to his nephew on securing the damnation of a human--''the safest road to hell is the gradual one--the gentle slope, soft underfoot, without sudden turnings, without milestones, without signposts''.
* In the Literature/FatherBrown stories, Father Brown persuades the GentlemanThief Flambeau to reform and become a private detective by convincing him that he's deceiving himself about the possibility of remaining a professional criminal without doing anything genuinely evil.
* In ''Literature/StarWarsKenobi'', [[spoiler:Orrin Gault]] is eventually revealed to be this. He started by embezzling money from [[spoiler:the Settlers' Call Fund in order to make payments on his debts. When attacks by Tusken Raiders became rarer courtesy of Anakin Skywalker, more and more settlers canceled their subscriptions, so Orrin and his family began [[MonsterProtectionRacket staging raids to make them return]]. They never give the settlers more than light injuries, but are not above killing actual Sand People in "retaliation". At the climax, he attempts to murder Ben after the latter witnessed them faking a raid and finds out he's a Jedi in the process; even so, Ben lets Orrin go, only for the latter to [[RedemptionRejection refuse to turn around]] and plan to sell Ben's identity to the Galactic Empire. His kids don't fall far from the tree and decide to kill Annileen Calwell, who had been the family's best friend until the day before.]]
* In ''Literature/TheIronTeeth'' web serial, Blacknail the goblin starts out small and weak. At first he sticks to petty crimes such as theft, but in order to gain power in his "tribe" of outlaws he begins to kill.
* A major theme of ''Literature/TheLostFleet''. [[OneNationUnderCopyright The Syndicate Worlds]] were a brutally repressive and unpleasant oligarchy to start with, but in [[ForeverWar a full century]] of bloody and seemingly unwinnable war, TheAlliance has started [[HeWhoFightsMonsters started resorting to tactics as ruthless and immoral as their enemies.]] It takes recently-defrosted HumanPopsicle Captain John Geary bringing an outside perspective -not to mention [[BerserkButton really blowing his stack in public]], [[OOCIsSeriousBusiness something he does no more than five times in seven volumes]]- to shock some of the other SpaceNavy officers into [[MyGodWhatHaveIDone realising just how far they've fallen.]]
* This trope got a nice lampshading by Jenny Bunn in Creator/KingsleyAmis' ''Take A Girl Like You'':
--> This business of why shouldn’t we do this, and we do it, and so then why shouldn’t we do this, and we do that, because it’s only a tiny bit more than the one before, and it would be so nice – it’s leading on and it’s not leading on, it’s like with a bag of sweets, just one more and we’ll put them away, except one more’s only just the one more, isn’t it? And they are nice, so there’s never anything against… Oh, all I mean is people forget things and lose their heads. You know how they do.

[[folder:Live-Action TV]]
* ''Series/TwentyFour'': This is one of of the main points behind Jack's arc in the final season: after losing another loved one thanks to the conspiracy of the season and being denied justice against her killers when the President of the United States betrays him, he '''snaps''' and goes on a RoaringRampageOfRevenge to slaughter everyone behind said conspiracy. The thing that kicks him down the path is when he executes one of those involved in the plot that didn't even have to do with the murder. After this, his actions get much more brutal and violent with each episode, with him even starting to unintentionally endanger innocent people as he slowly becomes just as bad as the villains. [[spoiler:Chloe manages to snap him back to his senses in the series finale before he crosses the last line and unwittingly starts World War III.]]
* ''Series/BoardwalkEmpire'': Jimmy Darmody has a conversation with his wife in the second season about how every time he draws a line in the sand, he winds up having to cross it to be a successful gangster. This eventually results in him doing all sorts of things he never thought he'd do, and that other people are horrified by, including [[spoiler:ordering the assassination of his father figure Nucky]].
* ''Series/BreakingBad'': [[ProtagonistJourneyToVillain The whole point.]] Walter White starts as a chemistry teacher who gets cancer, so he begins to make meth as a way to leave money for his family. Then, his actions become not only much less justified, but also he goes on to kill and begins some big schemes.
* Very common in ''Series/BuffyTheVampireSlayer'' and ''Series/{{Angel}}'', with examples including Faith, Warren and Amy. The heroes are also commonly battling with this themselves - Willow eventually turned evil for a brief but memorable period, and Wesley also got fairly dark.
** This got fully-developed with Faith - after accidentally killing a human on pure instinct before realising he was ''not'' a vampire, she tries to wash her hands of it (both metaphorically and literally) and convince herself (and others) that she truly doesn't care; then she tries to deflect blame on Buffy... Angel does a LampshadeHanging on this trope when he says that now that Faith has killed, "she's got a taste for it now"; when Wesley botches his attempt to talk her around she teams up with the Mayor, she falls deeper until she ends up in a coma. Eventually though, unlike Warren and Amy above, she becomes TheAtoner.
* ''Series/{{Merlin}}'': Morgana has a long-term one of these over the course of the second and third series. Of course, this is usually conveniently forgotten about when she is not directly the antagonist of each plot of the week.
* ''Series/OnceUponATime'': Regina becomes increasingly dark and angry [[spoiler:after her mother, Cora, kills her boyfriend]]. She has evil thoughts about killing Snow, who she blamed for her telling Cora about Regina, and Daniel. After she banishes her mother by using magic, she tells Rumplestiltskin "I'll never use magic again." He asks why, she says "Because I ''[[EvilFeelsGood loved]]'' it". [[StoicWoobie And she still manages to remain good]], despite [[TheDarkSide this causing an addiction]], and [[HeroicWillpower she refuses to obey Rumplestiltskin]]. Then, he gives her a HopeSpot to make her grow insane and think that she should get revenge because it is all she will believe that she has left to do. It works.
* ''Series/{{Revolution}}'': Ever since Rachel Matheson made a deal with the devil named Randall Flynn to ensure Danny's survival from birth ("[[Recap/RevolutionS1E7TheChildrensCrusade The Children's Crusade]]"), this trope has been happening to her. She killed the Wiry Stranger when he tried to steal food from the Mathesons ("[[Recap/RevolutionS1E2ChainedHeat Chained Heat]]"). She turned herself into Miles's custody to allow her family to escape his clutches ("[[Recap/RevolutionS1E4ThePlagueDogs The Plague Dogs]]"). She apparently refused to reveal or do anything for 7 years...until Danny ends up in Monroe's custody ("[[Recap/RevolutionS1E5SoulTrain Soul Train]]"). Then she reveals enough information to get her old colleague Bradley Jaffe and his daughter in trouble. She ended up killing Jaffe to save her own life and Danny's ("[[Recap/RevolutionS1E9Kashmir Kashmir]]"). She insists on destroying the pendants rather than letting Team Matheson use them. She pulls out a nanotech capsule from [[spoiler: Danny's corpse]] ("[[Recap/RevolutionS1E11TheStand The Stand]]"). She slapped Charlie where her daughter tried to call her out on leaving them all those years ago ("[[Recap/RevolutionS1E12Ghosts Ghosts]]"). On Rachel and Aaron's journey to the Tower, Rachel tries stealing the information she needs from her old colleague Jane Warren and nearly got killed for it ("[[Recap/RevolutionS1E14TheNightTheLightsWentOutInGeorgia The Night the Lights Went Out in Georgia]]"). Then she steals food from a tribe, shoots the tribe leader when he threatens to kill them, and gets in big trouble for it ("[[Recap/RevolutionS1E16TheLoveBoat The Love Boat]]"). Finally, she leads a family to believe that she can save their boy from death, and then reveals to Aaron that she's not trying to restore power for anyone's good, but rather to give the people the power to kill Monroe as revenge for killing [[spoiler:Danny]]. She is also willing to throw Aaron under the bus to achieve her revenge ("[[Recap/RevolutionS1E17TheLongestDay The Longest Day]]"). She has been sinking to new lows as the series goes on.
* ''Series/{{Smallville}}'': ComicBook/LexLuthor has this happen to him over the course of this show, going from close friend of Clark's and genuinely good guy to evil villain over the course of the series. Lampshaded when he tells Ryan that 'Evil is a journey, not a light switch'.
* ''Series/StarTrekDeepSpaceNine'': Gul Dukat was always a nasty authoritarian, but in early seasons would help the good guys on a pragmatic basis. After the Dominion War started, he aligned Cardassia with the Founders. When that didn't work, he became a full-on OmnicidalManiac.
* ''Series/KamenRiderGaim'': Kureshima Mitsuzane. He starts off as an overall nice guy, sidekick, and good friend to the Hero, and the brains to his brawn. As the series progresses, he starts showing a darker side to himself. [[spoiler:He begins attempting to manipulate his friends and outright lying to them, hiding vital information, and allying with the Yggdrasil Corporation they are against.]] While all this was done in order to protect his friends, he starts feeling that using those methods is the only way to accomplish that, and keeps doing so. Once Kouta, the series protagonist, starts unknowingly hindering his plans to keep everyone he cares about safe, he slowly starts to lose it and the situation gets even worse when his friends find out the truth and side with Kouta instead of him. Mitsuzane's solution to this development? [[spoiler:To ally himself with the resident Mad Scientist and shoot Kouta in the back while he's distracted. Although he fails to kill him, it gets worse from then on as he stands idly while his older brother is seemingly murdered, takes his Transformation Trinket and tries to commit first degree murder on Kouta once more while keeping the façade that he is his brother Takatora, who Kouta befriended not too long ago, and acting like he's still Kouta's best friend whenever they meet untransformed.]] To top things off: [[spoiler:After once more standing by and letting an ally get killed, even if that person was the Hate Sink of the series, he allies himself with Redyue, the resident Psychopathic Womanchild, and his acts get even more despicable. To the point that he's shown his true face to Kouta while trying to verbally break him and also beating him up untransformed. When Takatora shows up, still alive, and decides Mitsuzane needs to be stopped, they fight. Takatora hesitates in giving the coup de grace... Mitsuzane doesn't.]]
* It's been heavily implied in ''Series/DoctorWho'' that the Doctor is terrified of this happening to him. And in fact, during his first adventure, he almost killed a caveman with a rock, until Ian intervened. Which is why he likes to have humans around him at all times. Because they keep his bad side in check. Donna Noble's actions in "The Fires of Pompeii" was a good example.
* An interesting example with Tony Soprano in ''Series/TheSopranos''. He starts the series as a NobleDemon who tries to run the mob in a manner in which few people will get hurt. However as the show progresses, Tony becomes increasingly desperate to hold onto the power he's gained. This, coupled with the numerous things he suffers, causes the [[EvenEvilHasStandards standards]] he had to begin slipping away from him. By the series finale, he's effectively become a full-blown VillainProtagonist, albeit a self-aware one.
* ''Series/HemlockGrove'': Roman slowly becomes more immoral as time goes on. Early episodes where he shows his depravity such as him raping a girl from his school are initially offset by his horrible domestic situation and his perpetual self-loathing. By the end of the series he's become so unhinged that he's simply murdering people left and right, forcing Peter to finally turn against him.

* ''Afraid of the Dark'' by ''Music/TheMegas'' is about [[VideoGame/MegaMan3 Shadow Man's]] terror as he slowly loses his old personality and his reprogramming takes over. Midway through the song, the darkness actually starts singing to him.
-->''I feel it tearing me apart''
-->''Are you afraid of the dark?''
-->''I feel the shadow in my heart''
-->''Are you afraid of the dark?''

[[folder:Tabletop Games]]
* ''TabletopGame/{{Deadlands}}'' uses this as part of the two most extreme [[PayEvilUntoEvil Dark Gray Hat]] character types. Vampires, in Deadlands Classic, and Anti-Templars, in the post-apocalyptic Deadlands: Hell on Earth setting. Both have backstories that they will inevitably fall to corruption or die, and in a case of GameplayAndStoryIntegration, these are backed by mechanics that eventually determine when the player becomes invalid.
* In ''TabletopGame/{{Ravenloft}}'', performing an evil deed and certain other actions result in what is called a Dark Powers Check, to see if the forces that govern the Demiplane of Dread take notice. If they do, the Dark Powers simultaneously imbue them with a blessing and smite them with a curse. These powers and curses grow with each subsequent failed check, until inevitably the victim becomes a monster, perhaps even a DarkLord in their own right.
* The ''TabletopGame/ChroniclesOfDarkness'' game lines all have a KarmaMeter and take place in a CrapsackWorld rife with challenges that can threaten Morality degradation. Moreover, while {{Muggles}} can regain Morality for free through major acts of heroism, any supernatural PlayerCharacter has to spend precious ExperiencePoints from the PointBuildSystem to climb back up the slippery slope -- and they have more ways to lose morality as well. This struggle is especially applicable to ''TabletopGame/VampireTheRequiem'' and ''TabletopGame/DemonTheDescent'', which emphasize the characters' conflict with their inner, amoral, inhuman natures.

[[folder:Video Games]]
* A major theme in ''VideoGame/BioShock'', where the two Big Bads during the [[FlavorText backstory]] change from rude ruler to the people they hate most (in the [[VideoGame/BioShock1 first]], an objectivist became first a dictator, then a totalitarian dictator, in the [[VideoGame/BioShock2 second]], an Altruist became more and more selfish and [[spoiler:ends up sacrificing everything to save herself]]). The [[AnAesop lesson]] here is the danger of fanaticism.
** [[spoiler:Can also apply to Subject Delta in ''[=BioShock=] 2''. The "Lamb is watching" refers to Eleanor. And, sure, you do what you need to in order to get to Eleanor... but whatever you do, Eleanor will pick up from there. Harvest little Sisters? Kill [=NPCs=]? You watch in first person as Eleanor at the end of the game takes your lessons to heart.]]
* In ''VideoGame/MafiaTheCityOfLostHeaven'', Tommy starts off trashing a rival family's cars and finishes the game as a stone-cold killer.
* Arthas in ''VideoGame/WarcraftIII'' is initially a WellIntentionedExtremist when he decides to kill the citizens of Stratholme [[ZombieInfectee who ate infected grain which turns humans into zombies and would soon morph into the undead]]. After unwittingly [[DealWithTheDevil selling his soul to the Lich King]] in order to make use of the sword called Frostmourne, [[TheEvilPrince he kills his father, the king of Lordaeron]], destroys the elven capital of Quel'thalas, and aids in the opening of a demonic portal for the Burning Legion.
* In ''VideoGame/WorldOfWarcraft'', the [[BloodKnight war-mongering]] [[FantasticRacism racist]] Garrosh Hellscream started as a crude and needlessly aggressive leader who simply wanted what was best for the Horde. Over the course of his rule, he became increasingly harsh on non-Orc members of the Horde and began to dream of conquest, by whatever means necessary, alienating allies and uniting his enemies. His creation of [[TheHorde the True Horde]] and use of an Old God's power was the final step in becoming a villain.
** The Forsaken under Sylvanas have become more explicitly villainous after Sylvanas experienced TheNothingAfterDeath. In her drive to prolong her existence as long as possible, she has not only gone to extreme lengths to capture contested territories, but has also begun to turn on the Ebon Blade and even create new Forsaken by raising her fallen enemies as new Forsaken. Even ''Garrosh'' thinks she's going too far, but [[FantasticRacism that just may be his personal hatred of the undead]].
* Joshua Graham of VideoGame/FalloutNewVegas began as translator and missionary, but slowly compromised himself until he became known as one of the [[TheDreaded cruelest, most dangerous men in the Mojave]]. [[TheAtoner He gets better, though.]]
** Graham does, however, subvert the trope in his actual in-game appearance: although he has long since slipped into evil and been reformed, the conflict of his character arc in-game is seeing whether he can ''stay'' on the path of righteousness, or whether his hatred and rage will ultimately drag him right back down the same path again.
* ''VideoGame/SpecOpsTheLine'': [[spoiler:Walker's]] entire character arc is one of these.

* In Book 9, Part V of ''Webcomic/SchlockMercenary,'' General Xinchub is revealed to have gone through one of these:
-->'''Xinchub:''' I sold my soul a long time ago, believing that I was helping Humanity, and all our Terran cousins. I've done all kinds of atrocious things, and somewhere along the line I started to enjoy them.
-->'''Ceeta:''' Happy memories?
-->'''Xinchub:''' Yeah, good times, good times.

[[folder:Web Original]]
* In ''WebVideo/DoctorHorriblesSingAlongBlog'', Dr. Horrible starts off as an [[IneffectualSympatheticVillain ineffectual]] AntiVillain, maybe with [[WellIntentionedExtremist good intentions]], but through constant humiliation, [[LoveMakesYouEvil losing his love interest]] to the {{Jerkass}} SmugSuper Captain Hammer, his own urge to join the Evil League of Evil, and the League's threat that he [[IfYoureSoEvilEatThisKitten prove himself by killing someone]] or be killed by the League for wasting their time, he takes a long ride down the evil slope, culminating in the attempted murder of Captain Hammer.
* The trope comes up a few times in ''Literature/{{Worm}}'':
** [[http://parahumans.wordpress.com/2012/05/17/interlude-10-5-bonus/ Armsmaster's description of Skitter's career fits the template.]]
*** Armsmaster's description, however, neglects to mention the detail that [[spoiler:he was using her to spy on the Undersiders for his own gain.]] The truth is that she wasn't evil until he pushed her away.
** One of the people Skitter recruited in the wake of [[spoiler:Leviathan decimating the town]], Sierra Kiley, mentions in her narration during [[ADayInTheLimelight Interlude]] [[http://parahumans.wordpress.com/2012/10/11/interlude-14/ 14]] that she worried that Skitter would try to lead her down this path, and was [[AvertedTrope surprised it hadn't happened.]]

[[folder:Western Animation]]
* Creator/SethMacFarlane likes this trope, although he [[PlayedForLaughs plays it for laughs]]. He's {{Flanderized}} two of his star characters, Peter Griffin of ''WesternAnimation/FamilyGuy'' and Roger Smith of ''WesternAnimation/AmericanDad'', into FauxAffablyEvil {{Jerkass}}es. Roger's DisproportionateRetribution to Steve for taking his cookie was arguably the start of his crueler aspects taking over his role, while Peter's probably began with the lighter abuse of Meg in early post cancellation episodes.
* Megabyte from ''WesternAnimation/ReBoot'' is an interesting example. He's already a villain at the start of the series, but he's nothing but an AffablyEvil NobleDemon who's "Take Over The Supercomputer" schemes get foiled every week. However as the show goes on and he becomes more desperate to succeed, Megabyte becomes increasingly amoral and willing to do ruthless things. He finally crosses the line into true villainy when [[spoiler: he exploits Bob's belief that Megabyte was redeemable to banish Bob from the Mainframe.]]

[[folder:Truth In Television]]
* The subject of [[http://www.nova.edu/ssss/QR/QR9-2/oleson.pdf this journal article]] made friends with a drug dealer, then started to help him run his gang, then shot a man in self-defense... By the end of his criminal career, he had killed fifteen people and was prepared to commit murder merely to "safeguard his reputation."
* A variation with "careless" instead of "evil": The "deviation normalization" principle. A high risk system, such as a spaceplane, is designed to work in some way. Then, something unexpected happens. There's a little problem, but it's rationalised as "unfixable" and "unimportant". It's just something that has always been happening, and it becomes the new standard. These little problems accumulate over time and, eventually, something turns out to be more important than thought and all goes horribly wrong. Case in point: Challenger [[note]]O-rings, rubber seals on tanks, would sometimes be damaged by the heat. This happened for over a dozen times, but was considered unimportant (it's always been like this...). Then, once, when there was very cold weather and the seals became brittle, they didn't hold, fuel escaped and Challenger exploded.[[/note]] and Columbia [[note]]A piece of foam got loose during the launch and pierced a hole in the heat shield. Two problems: It was known that foam sometimes gets loose, but it was believed it can't do harm; The software used to determine damages by the hit was outdated and wasn't callibrated, yet it was used anyway. This led to Columbia falling apart during reentry despite the problem being known.[[/note]] .