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->''"Irresponsible ''children.'' My patience is stretched ''miles'' beyond its threshold. Embrace your wounded; you will be joining them in ''hell.''"''
-->-- '''The Wanderer''' [[http://www.itswalky.com/d/20020721.html makes his entrance]], '''''[[Webcomic/RoomiesItsWalkyJoyceAndWalky It's Walky!]]'''''

In order to [[CerebusSyndrome add more drama to a series which has been, up until that moment, lighthearted and comedic in nature,]] a villain is introduced which is played completely straight, in contrast to the [[HarmlessVillain bumbling and comedic villains]] the heroes have faced before.

This villain's arrival is usually heralded by a sudden downturn in humor, to show the audience this guy means business. In other words, a catalyst for a drastic change in mood toward the dark and dramatic.

In some depictions, particularly LighterAndSofter ones, said villain may still have [[LaughablyEvil some light-hearted or comical traits]], but still gives a much higher sense of dread and genuine threat to the heroes than previous adversaries. Some cases of the trope may be harder to define by comparison in a particularly ineffective RoguesGallery, though a clear cut example at the very least can actually place the protagonist in real danger compared to the HarmlessVillain that [[PokeThePoodle poked his poodle]] in a previous arc.
A typical symptom of CerebusSyndrome.

A Knight of Cerebus is very likely to be DangerouslyGenreSavvy, but also runs the risk of becoming a VillainSue. Arguably a subtrope of ThresholdGuardians. See also DeadSerious, NotSoHarmlessVillain. The show may ShooOutTheClowns first. Often, this results in a case of VileVillainSaccharineShow. When this kicks off CerebusSyndrome, his arrival is a GutPunch. Sometimes, this type of character can be a CompleteMonster if they have no redeeming traits and do terrible things by the standards of history in an initially more lighthearted series.

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!Examples:
[[index]]
* KnightOfCerebus/AnimeAndManga
* KnightOfCerebus/ComicBooks
* KnightOfCerebus/FanWorks
* KnightOfCerebus/{{Film}}
* KnightOfCerebus/{{Literature}}
* KnightOfCerebus/LiveActionTV
* KnightOfCerebus/VideoGames
* KnightOfCerebus/{{Webcomics}}
* KnightOfCerebus/WebOriginal
* KnightOfCerebus/WesternAnimation
[[/index]]
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!!Other examples:

[[foldercontrol]]

[[folder:Radio]]
* ''AdventuresInOdyssey'' is largely a realistic show about realistic small-town problems, that had a few forays into serious territory early on, whether it was an adaptation of a Bible story or a robbery... but when Dr. Blackgaard showed up, things ''changed''.
[[/folder]]

[[folder:Roleplay]]
* The Cult of Apophis in ''RolePlay/YuGiOhEastAcademy'' presents a very real and significant danger to the heroes; their appearance marks the darkening tone of the RP.
[[/folder]]

[[folder:Theater]]
* ''Theatre/{{Camelot}}'' is extremely lighthearted up until Mordred arrives, and then starts building toward a genuine tragedy. This could easily have caused MoodWhiplash, but it's handled extremely well.
* Also in ''IntoTheWoods'' when the female giant shows up in act II, lets just say things go down hill from there.
* Don John from ''MuchAdoAboutNothing'' is definitely a VileVillainSaccharineShow and his EvilPlan causes CerebusSyndrome to kick in.
[[/folder]]

[[folder:Professional Wrestling]]
* Wrestling/NewWorldOrder. They debuted in one of wrestling's most cartoony eras and proceeded to utterly annihilate every face who stood in their way. They were led by Wrestling/HulkHogan, formerly an InvincibleHero, now a cruel and vindictive hell who loved to play the numbers game. Hell, they were so dark that Sting went through a personality 180 from a cheery surfer from a brooding Crow-type just so he could effectively combat them!
* Wrestling/TheUndertaker's Wrestling/MinistryOfDarkness. They crucified and hung their enemies, kidnapped women, brainwashed midcarders, made blood pacts in the middle of the ring... only infighting and The Undertaker getting injured put an end to them.
* Wrestling/TheNexus made their debut by savagely beating down everyone around the ring- and we mean ''everyone''. The faces, the heels, the trainers, the announcers, the commentators... they even destroyed the ring! Wrestling/RAW ended with the seven of them standing tall, everything around them utterly annihilated. [[FromBadtoWorse And it got worse from there.]]
* Wrestling/TheWyattFamily. With the WWE's current LighterAndSofter atmosphere, it's really jarring to see a gimmick like this one, especially considering it may be one of the most disturbing and genuinely unnerving characters in the history of the company.
--> "Hey, wanna see something... really scary?"
* A well-booked MonsterHeel usually qualifies, since they will steamroll face after face until someone puts them down. Well-known examples include Wrestling/BrockLesnar, Wrestling/MarkHenry since his 2011 FaceHeelTurn, and even Wrestling/BethPhoenix.
* Wrestling/TheShield. While they've started to fall apart in 2014, they debuted as a brutal SWAT Team-like trio who would steamroll anyone with flawless teamwork and then Triple Powerbomb them through a table.
[[/folder]]

[[folder:Other]]
* [[BigBad Makuta]] from ''{{Bionicle}}'' started out [[EvilOverlord menacing enough]], but his constant defeats and failures gradually robbed him of his credibility. After the original head of the Story Team left, the character of Makuta underwent a serious retcon, which resulted in him turning into a [[TheChessmaster calculating]] mastermind who had [[XanatosGambit planned his victory]] from the start, turned out to be the BiggerBad behind a lot of former villains, and by the end of the story arc, ended up ''[[TheBadGuyWins winning]]''.
* ''Franchise/{{Noob}}'' is set in a {{MMORPG}}, so the early villains, while annoying and sometimes geunine thearts in-game, were no longer a problem once characters logged off. Then enter Master Zen, who had a deep resentment against the protagonists and is willing to after them in real life. A plot present in all three incarnations of the franchise included him breaking into one of the protagonist's appartement, while the webseries had him resort to kidnapping and the comic showed outright (but fortunately failed) murder attempts.
[[/folder]]

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