Bart: Oh, it's you, Bob. How' ya doin'?
Sideshow Bob: No screams? ... Not even... an "eep"?
Bart: Hey, I'm not afraid of you. Every time we tangle you wind up in jail!
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- In a stunning and awesome inversion, Dungeon Keeper Ami features Mukrezar. Mukrezar is, and was, a Keeper of dubious competence, given to many Zany schemes (usually involving a Ring of Power). However, since his resurrection he has shown such an assessment is significantly lacking. Apparently his resourcefulness, ability to bounce back from crushing defeat, and, most importantly, willingness to take incredible chances- and then turn them into victories even if they failed -was his greatest asset. Every appearance has only increased the estimation of his threat, despite being Plucky Comic Relief.
- In the beginning of Snow Angels, Disaster is introduced as an almighty being capable of driving people to madness just by seeing it. For a short while the heroes (who include a time traveler and Sufficiently Advanced Alien) actually have trouble fighting Disaster, but by the end of the first arc, Disaster has decayed so much that it's beaten up by perfectly-mundane schoolgirls. Ironically, Disaster is the same entity as Sasaki, so she actually received an upgrade before the decay.
- My Little Unicorn:
- Discord, god of chaos and in general considered one of the best characters in My Little Pony: Friendship Is Magic, is reduced to a brainwashed monster henchman of Big Bad Titan near the end of the story and loses his reality warping abilities. To add insult to injury, he gets Killed Off for Real by Celestia.
- The sequel also does this to Queen Chrysalis.
- Harry Potter has Voldemort, who suffers a severe case of this in The Ariana Black Series. In canon, he's practically a personification of Nightmare Fuel. In the fanfic, he's just an incompetent mustache-twirler.
- Subverted in Ultimate Sleepwalker: The New Dreams or Ultimate Spider-Woman: Change With The Light. Given that the Sorting Algorithm of Evil does NOT apply in these series, and the heroes do not gain any new powersets or power boosts over the course of the series, villains who were introduced early on have remained constantly and deadly threats throughout both series' runs. In fact, the author has specifically gone out of his way to ensure that this trope is subverted by allowing villains who look like they might suffer from this trope to actually succeed in their evil plots.
- Young Justice Darkness Falls: Depending on what you might think about The Light, you could say they underwent a form of this, since a lot of their subtle manipulations, small progresses and the like gets thrown out with what seems like Vandal Savage's nest egg plan to use Darkseid as HIS endgame. And then when Luthor cuts off the Light's legs by giving the league information about their operations, the Light essentially goes into hibernation for the most part, with any plans they have either done in public by Luthor or done by brute force. But even then, Klarion wasn't working for the light that time.
- Whenever a new army in Warhammer 40,000 is introduced, they start as existential threats to the entire setting for a year or two and then decay into just another faction.
- There's an obvious reason for this: profit. Make your new faction unstoppable arse-kickers who make mincemeat out of any opposition, and you've got a surefire way of getting eternal 13-year-old boys everywhere forking out on them just so that they can be the toughest tabletop warrior. Then throw out some heroic last stands for the Space Marines so that the existing factions don't get completely alienated. Wait a few years till everybody's got them, introduce a new, even more powerful, even more expensive faction. Rinse and repeat. Profit.
- Necrons. When first formally introduced, they were supremely enigmatic horrors serving even more horrific beings, known for mysterious harvests of life, unknown plans, and ridiculously advanced technology. Fan perception of them quickly made them Omnicidal Maniacs to the public eye, and they began to be perceived as a race-wide Creator's Pet. The 5th Edition Codex has resulted in a serious hit to the Necrons' previously unknown and unstoppable nature in favor of shifting the focus towards the Tyranids and Chaos as the greatest threats facing humanity.
- The Orks started off as a galaxy wide tide of death and destruction but degenerated into pub brawlers over time.
- Zigzagged with the Orks. No one in the setting, and very few outside of it, will argue that Ork hordes aren't a serious, ongoing threat to everyone else. The problem is, Orks have kinda been stuck in the status quo area for a while, and the big video games featuring them have them on the bottom of the Villain Pedigree.
- Tyranids also started off as unstoppable, galaxy-devouring horde of alien locusts, but their impending, full-scale invasion and eating of the galaxy kept getting delayed and delayed and then the tyranids inexplicably adopted an "attack in small numbers" strategy that made them less of a threat to the setting.
- Then on a smaller scale you have some of the lords of Chaos. Abbadon the Despoiler is probably the number one offender. He is supposedly the heir to Horus and carries the title of Warmaster of Chaos, as well as the favor of all four Chaos Gods. However his Black Crusades seem to end in defeat more often than not, or at best as a stalemate. One can argue on whether or not it's his fault but the community at large now looks at him as a bit of a joke, earning him the nickname Failbaddon.
- Games Workshop has spent the better part of 2013 trying their hardest to dispel this notion about Abaddon, eventually resorting to retconning eleven of his thirteen Black Crusades.
- In any table top rpg with a significantly steep power curve, this can happen rather quickly. Dungeons & Dragons (and Pathfinder) are the best known examples, where an enemy which is an absolute terror at one point could be a beatable boss a few levels later and a mook a few more after that. If the villain doesn't scale to the power level of each Player Character, this trope becomes almost inevitable.
- Blood Boy, a big antagonist in the early stages of Survival of the Fittest version 3 had this occur in the last topic he appeared in, becoming an almost Jokeresque figure (to the point of almost directly quoting from The Dark Knight at one point). This does, however, have a fairly good reason: a different handler took over the character for that scene, one who, needless to say, had a rather different take on the character.
- The Necromancer, in the Whateley Universe. Starts out as one of the top 60 supervillains on the Interpol rating scale. He's now oh-for-two against Team Kimba, who are high schoolers. Even with his team of supervillains working for him. Now one-for-two, making out like a bandit in the process, excluding one goal failing due to a Unknown Unknown.
- On TWGTG, we have the Mad Scientist Dr. Insano that first appeared on The Spoony Experiment, whose early appearances depict him as a Laughably Evil, but none the less dangerous character. Later appearances, however, have him attempting no evil plans and just have him acting comedic.
- Averted with Atop the Fourth Wall's villain Mechakara, who is presented as a Knight of Cerebus that almost kills Linkara in his first appearance, and when he later reappears, despite being Demoted to Dragon for the new Big Bad Lord Vyce, he's become even more a threat due to being upgraded, shown most notably in that his re-match with Linkara he No Sells the methods used to defeat him the first time. (And then in To Boldly Flee, he not only takes out Linkara in five seconds, but comes within an ace of killing the entire TGWTG cast.)
- The suave, chessmaster-like, psychotic Ask That Guy is slowly turning into a pathetic, needy, emotional wreck. Maybe played with because he's always been like that, he just can't seem to hide it anymore.
- In his first appearance during the Nostalgia Critic's review of The Last Airbender, Shamalayan removed Critic's talent (he gets it back, even though "there wasn't much to lose"), and would have done it again in Devil if he hadn't been stopped by the actual Devil. Come After Earth, and he's become so predictable that Critic isn't even phased by him anymore.
- Strong Bad, from the infamous Homestar Runner universe, used to try to do actually evil things, but he's gone under lots of Villain Decay. To quote him from the Strong Bad Email(sbemail) called "your edge"
Strong Bad: Me and the Cheat, walked past this deflated basketball and consciously decided not to re-inflate it! And we feathered Strong Sad for a HALF HOUR!
- In Noob, Dark Avenger is one of the most feared player killers of the game... except a Running Gag has Sparadrap accidentally killing him. He's shown to give other characters difficulty, but it made the decay slower rather than keeping it from happening. Writing Dark Avenger out of the series due to his actor moving away relied on having that decay reach the lowest point possible.
- The C.C Corporation in Flander's Company started out as a relatively competent organisation who actually succeeded in taking over Trueman's company without him even noticing, and their leader Carla Burnelle was a Psycho Electro and Magnificent Bitch who could handle the whole team of protagonists of her own. Come season 3, the arrival of Aegis cause Carla to suffer a Villainous Breakdown, leading her to a Genre Blind decision. Her group is even worse, as most competent members are either Killed Off for Real or Put on a Bus, leaving her more and more Surrounded by Idiots.