So you are planning on a series where every episode your hero will fight a different opponent. But you also want to show him as a nice soul that wants to help any extra that crosses his path, so you want to add a victim as well, but that seems too crowded for a single episode, wouldn't be better if you could condense it a little? Maybe by combining up some things?
Enter the Villain-Possessed Bystander. Instead of creating his own monsters, or fighting directly, the villain will take a random person from the audience and transform them into a minion. This can be really convenient in a family-friendly show since it creates an in-universe reason for not killing them. These are normal people that cannot help themselves so the duty of The Hero is not only to stop them, but help them get back to normal. This trope is quite common not only for Tokusatsu and Sentai fare, but also for Magical Girl shows, though it's also started showing up in more western shows as well.
Since the villain creating monsters from literally any random person would be too powerful, and because the villain needs to be, you know... a villain, in most cases the selected victim tends to be someone that recently suffered some kind of distress, most likely emotional so, while they may be willingly lured into helping, once the transformation takes place they tend to be too controlled by the villain to make any real choice (though exceptions might apply).
While it can be used a single time it tends to work better in a Monster of the Week format as the villain's Modus Operandi (or at least a frequent strategy) since it provides more time to know the victim, and allows for the use of more victims as well. And while is normal for a villain to be the one responsible for this, is not necessary; it could be natural or caused by a non-sentient force, as long as someone can be infected (and it can be solved in a single episode).
This always involves Super Empowering, likely relating to the emotional distress of the victim. May overlap with Hijacked by Ganon if a new villain was actually empowered by an old one. May involve Demonic Possession, which usually involves the hero having to Beat the Curse Out of Him. Sometimes possession can backfire on the villain, such as becoming Trapped in the Host. Compare Clone by Conversion, Reforged into a Minion, Face–Monster Turn and Break the Cutie. Contrast Not Me This Time, when a new threat actually is unrelated to the common villain despite initial thoughts.
- Corrector Yui presents an interesting case in which not even the corrupter is at fault. In this case is a little girl who happens to be a virus, so whenever someone interacts with her, their code gets infected and become monsters.
- In Cute High Earth Defense Club LOVE!, every Monster of the Week is a random school student, who turns into a monster after being mind-controlled by the Big Bad Lord Zundar. These monsters tend to have gimmicky powers based on the student's one known personality trait, and they always turn back into a regular student after being defeated by the Battle Lovers.
- Flint the Time Detective combines this with Gotta Catch Them All. Flint and company need to collect all the Time Shifters so they don't damage the timeline. These are nice creatures not doing it on purpose, but the villain, Petra Fina, uses a rubber stamp to control and transform them into hideous monsters called Con forms which the heroes must revert through the Power of Friendship.
- This is the villains MO in the first 26 episodes of GaoGaiGar, where the Monster of the Week is a human infected with Zonder Metal combined with nearby materials. The role of Mamoru Amami is to purify the victims, due to being a Human Alien designed to counter Zonder Metal. The later episodes reveal the true masterminds, and that their goals are an in fact an Assimilation Plot.
- Anubis from JoJo's Bizarre Adventure: Stardust Crusaders. It's an Empathic Weapon that possesses its wielders, including random townspeople, a child, and Polnareff, forcing them to attack the Crusaders.
- In Powerpuff Girls Z this comes about due to a substance that the professor created. He used it to destroy an iceberg, but then beams infused with this substance hit many other people or things, but they tend to remain oblivious and keep their normal lives until they suffer a letdown and then the powers activate. An interesting case since this can not only affect people but also animals and even inanimate objects. Then this later turns out to be due to the presence of Him who was sealed away in the aforementioned iceberg. Once released, he creates monsters of the week through his "dark spores" possessing anyone (or again, anything) he senses is emotionally vulnerable.
- Has happened in various entries of Pretty Cure
- HeartCatch Pretty Cure! has people with wilting Heart Flowers turned into Desertrian (the Monster of the Week, combined with an inanimate object) who the Cures need to purify. Notably, both Erika and Itsuki were Victims who then became magical girls themselves.
- Doki Doki Pretty Cure has a similar concept, where people with selfish hearts called Psyches turn dark and become Jikochuus. Notable, the villains enhance or corrupt the victims' selfishness with force. In contrast to Heartcatch, almost every victim is just a random bystander.
- The Black Rose Arc of Revolutionary Girl Utena features minor, often comic relief characters such as Kanae and Tsuwabuki temporarily becoming duelists and attempting to kill the Rose Bride after having a "counseling session" with the Arc Villain Mikage, who gives them a seal that allows temporary access to the dueling arena. The characters generally dramatically change personality and become somewhat Brainwashed and Crazy after talking with Mikage about their problems.
- In the Stars season of the original Sailor Moon anime, after the Victim of the Week has their Star Seed removed from them, their bodies transform into a Phage, the season's Monster of the Week. Sailor Moon luckily has upgraded her powers in order to transform the Phages back so their Star Seeds can return to them.
- This is the general format of Yu-Gi-Oh! ZEXAL: Yuma and Astral are trying to collect the Number cards to restore Astral's memories, and the Numbers have a nasty tendency of being found by various random Duelists and driving them insane.
- Wonder Woman (1987): While supposedly locked up with his powers disabled Doctor Psycho takes possession of a series of innocent bystanders, forcing them to attack cops, mock Wonder Woman, relay his creepy infatuation with her and then jump to commit suicide while he mentally jumps to another bystander while she saves them. They're not empowered by Psycho but they do keep her busy as she fights and rescues them.
- X-Men villain Malice can exist as a being of pure psionic energy that can merge with the mind of another sentient creature. While people are possessed by her, a black necklace/choker with a silver medallion appears on the victim.
- Malus, the Fallen Angel Big Bad of Rachel Rising, is an intangible spirit that can possess the body of almost anyone, remains in them until the host dies (usually as a result of the things Malus forces them to do), and then moves on to the next. Anyone possessed by him gives no outward sign or indication that they've been taken over, except for their changes in behavior.
- The villain of Fallen is a demon named Azazel who possesses people through physical contact and has complete control of them until he moves on to a different host. Most of the people he uses as criminals and murderers were completely innocent people before he got to them, and after he leaves they don't remember anything from the possession, leaving them utterly confused. At one point Azazel possesses a man and pulls a gun on Denzel Washington's protagonist and threatens to shoot. He kills the man in self-defence, only for Azazel to simply jump to a new host as the man dies and walk off scot-free while Washington has to deal with shooting a schoolteacher who never did anything illegal in his life. At the end of the movie Washington has lured Azazel to a remote mountain cabin and kills all of his hosts and himself, knowing that after death Azazel has limited time to find a new host. But Azazel finds a cat to possess and smugly heads back to civilization, all the death and tragedy to stop him having been for nothing.
- This is the modus operandi of Agents in The Matrix series. Anyone who is still plugged into the Matrix can be possessed and transformed by an Agent at any time. Unlike many examples of this trope, our protagonists do not hesitate to kill those possessed by Agents in self-defense. If they can land a shot.
- Kamen Rider
- In Kamen Rider Den-O, the monsters are Jerkass Genies who distort peoples' wishes (which are, with perhaps two exceptions, well-intentioned or merely misguided. The Hero, a very compassionate young man, makes helping the Victims as much a priority as fighting the monsters.
- Kamen Rider Double features humans who become Monsters of the Week through Gaia Memories. However, these memories are addictive - Memory users go crazy the more they use them, and they can even suffer withdrawal symptoms when they try to stop using them. More than one monster in the show starts out with innocent intentions, but are driven mad by power and addiction.
- Kamen Rider Fourze has the MOTW, which is created by a human "Switcher" using a device called an Astro Switch; the Switcher is someone with a grudge who's so hell-bent on revenge that they're blinded to the fact that the Switch will eventually kill them. So instead of just beating up the MOTW, Fourze and his team reach out and try to befriend the Switchers so that they know there's somebody who cares.
- Kamen Rider Saber has the evil organisation Megiddo create new Megid by implanting blank books into people who can see the Wonder World. Notably, Mei, the female lead of the series, becomes one known as the Neko Megid.
- Super Sentai/Power Rangers
- Mighty Morphin' Power Rangers: In episode "Attack of the 60' Bulk", Bratboy is actually Bulk transformed by Rita and Zedd's magic.
- In episode 24 of Bakuryuu Sentai Abaranger, Giganoid #6: Giant, is just the Abarangers' friend Emiri made into a giant.
- In Kirby 64: The Crystal Shards The first three bosses Kirby encounters are the friends that will help him along the game. All of them were too close to one of Dark Matter's pieces and got possessed to attack Kirby.
- Happens twice in The Legend of Zelda: Twilight Princess. Fire boss Fyrus, who is actually Goron Patriarch Darbus; and ice boss Blizzeta, who is a yeti woman named Yeta. Both keep helping you after their defeat.
- Mega Man Star Force: Since the current incarnation of Mega Man is a boy who merges with an (Energy Being) alien, most of his enemies naturally consist of other humans who merge with other similar aliens. Specifically, the FM-ians in the first game prey on those with loneliness in their hearts, convincing them to allow themselves to be possessed.
- One-Punch Man: It's heavily implied that most, if not all, monsters exist because of the mysterious entity known as 'God'. We have seen humans, animals, and even inanimate objects undergo monster transformations, usually after going through extreme emotional distress. Unfortunately, there is no known way to reverse this process, so the heroes usually have no choice but to kill the monsters, even those who were once innocent people.
- The "New and Old Flames" arc of El Goonish Shive involves an unknown person summoning monsters that attack different parts of Moperville. The summoner turns out to be Dex, one of the comic shop regulars who was mind-controlled into the act by an Immortal.
- Generator Rex villain Van Kleiss gains the ability to do this after he undergoes a power upgrade. Nanites permeate the entirety of the world and Van Kleiss can cause them to go nuts and turn people and animals into monsters to fight Rex, one such victim being Rex's best friend. If Rex doesn't cure them in time these unstable mutations will become permanent.
- The second season of Jackie Chan Adventures has the characters working to keep the Demon Sorcerers from coming back to the mortal world. The fifth season has them attempting to recover the ancient artifacts originally used to seal them. These are imbued with the energy of their respecting demon, and if anyone handles them without magical protection, they absorb their power and appearance.
- This is the modus operandi of Hawk Moth, the Big Bad of Miraculous Ladybug. He can sense strong emotions and create "akumas", dark butterflies that seek out those consumed by negativity and transform them into supervillains with vast new powers and zero moral or emotional restraint. He promises his victims the chance to fulfil their desires, most often for revenge against whoever or whatever upset them, in return for retrieving the Miraculouses of Ladybug and Cat Noir. He is actually the holder of the Butterfly Miraculous, whose true purpose is to create heroes from ordinary people, but he twisted its power towards his evil ends.
- In Randy Cunningham: Ninth Grade Ninja, the Sorcerer has the ability to "Stank" any person that has been heartbroken or is going through emotional trauma, and transform them into a monster. They can be "destanked" by destroying what they hold most dear (usually an object).