Antagonist's Weakness

It does not matter how notorious antagonist can be, as every one of them surely have at least one weak point. Without this weakness, the story would not be nearly as interesting as it is. Exploring each antagonist’s weakness can be an important endeavor to defeat them.

Alongside heroes, antagonists have been around for generations as obstacles that the good must overcome. Like gooddoers, evildoers can also boasts special powers that they can abuse to kill or oppress everyone. Fortunately though, they still have some Achilles' heel that would be the key to stop them. The said weakness not always related with what they can do, but that include their loves one like the girl of their dreams, family, friends and most important, being in love with or without thinking what if the heroes found out. Their loved ones can be either their weakness or the key to put them back to the good side.

Marvel Cinematic Universe

 * Ultron: Ultron's weakness is lack of spare robotic bodies and stripped from Internet. He also cannot uses robotic bodies that rendered useless due to either dismembered or having the vital part (in his Ultimate Ultron Body, mechanical heart) removed.
 * Hive: As a result of gained memories from countless host bodies that he possessed over the course of his lifetime, Hive cannot let the said hosts' memories to be jumbled or else he would experience them all at once. If this happened, he would losing his identity and sanity as he wind up to struggle to speak sentences and instead say things said by previous hosts.
 * Aldrich Killian: Aldritch Killian's weakness is his arrogance and immature personality that ultimately contributing his death in the end. In fact, these personality traits has resulting him unknowingly staged his own downfall: The attempt to demoralizing his nemesis Tony Stark aka. Iron Man by using Extremis on his love Pepper Pots has resulted Pepper gained more than enough power to destroyed him in the end.

Star Wars

 * Emperor Palpatine: In spite of using Anakin's concern over his loved ones to turn him into Darth Vader, Palpatine ironically had no idea about concept of love that can bring bad guy like Vader back to the good side, let alone Goodness and Light Side of the Force. In fact, the attempt murder of Luke turned out indirectly pushed Vader aka. Anakin back to the good side that it provoked Vader to commit Heroic Sacrifice by tossing Palpatine into Death Star core in the first place.

Anime and Manga

 * Crocodile: Like those who gained supernatural power from Devil Fruit, Crocodile's powers can be hampered by water and other liquids include blood. Ivankov later found out a precious weakness of Crocodile's which he later used as blackmail.
 * Emperor Tathagata Killer: Being God's one true antithesis, Tathagata Killer can only be destroyed by his light counterpart and all good and faith in humanity regardless of their beliefs. This was hinted through his attempts in erasing religions throughout his conquest.
 * Kyuubey: It can be inferred that Kyuubey and his fellow Incubators' fatal flaw is their lack of emotion, which is the reason why they single-mindedly manipulating young girls to become magical girls and subsequently, witches, to complete a quota to prevent the impeding heath death of the universe at the expense of their well being and cementing them as abstract entities that beyond morality itself.

Western Animation

 * Sheldon J. Plankton: His weaknesses are flaws on his evil plans and his small size, which made only certain few (namely SpongeBob, Patrick, and Krabs) well aware with what would happened should he succeed.
 * Mr. Krabs: Krabs' greed and obsession with money, and viewing money as often anthropomorphic being sometimes proved to be his worst weakness, as the said greed get best of him as well as potentially drove him to perform appaling acts just as meant to improve his business or satisfy his unhealth obsession. This also worsened his rivalry with Plankton where Plankton even so appaled that be began to questioned how evil he was when comparing himself with Krabs.
 * Unicron: His only weakness is the power of the Autobot Matrix of Leadership which is the only key and weapon to destroy him.

Live Action Films

 * Predators: Though they are very difficult to kill, Predators would be more vulnerable should their cloaking system that made them invisible damaged. Also, due to their heat-based vision, they would had difficulty to see creatures that covered their signature heat via mud or incapable to produce heat at all (like Xenomorphs), forced them to rely on various vision modes on their masks.
 * Zombies (Night of the Living Dead): The best way to kill zombies or prevent a dying person to reanimated into zombie not long after his/her last breath is by damaging their brain.
 * Cain aka. RoboCop 2: Even after turned into robot, Cain is still retained his obsession with his Nuke drug. RoboCop then used this against him upon learned the robot's identity from one of his dying followers and notice his robot self's obsessive behavior on a vial of Nuke drug.
 * King Ghidorah: King Ghidorah had 2 weaknesses:
 * Had he immediately freed from his master's mind control, he would been left severely disoriented.
 * The loss of his middle head (the head which the most dominant out of 3 heads) also left him severely disoriented and vulnerable worse than freed from brainwashing, since his two other heads required guidance from the middle heads.
 * Indoraptor: The Indoraptor had two flaws:
 * He was compelled to follow a pre-installed targeting sequence via laser sights and auditory cues, meaning he could be led into traps by using his own relentlessness against him, which allowed Blue to push him through the glass roof to his death.
 * He was ultimately still in a prototype stage and not as effective as a final version of the hybrid, which was the reason why he was not ready for the Lockwood Manor Auction. That fact also could've been why Blue was able to put up such a fight against him and kill him so easily despite the Indoraptor being designed to outclass her in every way.

Animated Films

 * Hopper: Hopper was extremely afraid of birds, natural predator of insects in general.
 * Archibald Snatcher: Snatcher's weakness is his obsession with cheese in spite of being lactose intolerant.
 * Kai the Collector: Kai has an army of Jade zombies ("Jombies") and what can see what they see by briefly possessing them. Po uses this as an advantage to weaken Kai by distracting him so he can try using the Wuxi Finger Hold on him.
 * Cy-Bugs: Are weakened by the sight of light which attracts them and can lead them to their deaths.
 * Turbo: After becoming a Cy-Bug, Turbo's new Cy-Bug programming gave him the weakness of being attracted to light which Wreck-it Ralph used as an advantage by erupting Diet Cola Mountain, leading Turbo to his death.

Television

 * Azazel (Supernatural): In spite of his better resistance against anything that weakened normal demons, Azazel proved to weak against powerful artifact such as The Colt, powerful angels, angel knives, and demon blade. However, only the Colt that confirmed that he weak against.
 * Phantom Shadow (Scoobynatural): Iron can burn it, whether it be a simple candlestick or a long chain.

Videogames

 * Las Plagas: These parasitic lifeform's weakness is ultraviolet ray, which can kill them even after having their resistance to bright light enhanced.
 * Alex Mercer: Alex Mercer had numerous weaknesses due to his viral physiology:
 * His presence can be detected via viral detectors due to his viral physiology even when disguised.
 * Karen Parker's experimental parasite that created to make an antidote for Blacklight Virus would stripped him from most of his powers and would killed him if not cured in time.
 * Alex would be more vulnerable should he suffer serious injuries should he was succesfully dismembered or reduced into bloody mass, resulting him forced to assimilate other lifeforms to regenerate.
 * James Heller: Because he was enhanced by Alex Mercer with his own virus, James share both strengths and weaknesses (though how worse Karen Parker's experimental parasite's effect on Heller's body remained unclear with the parasite itself never used against him). His daughter also served as his weakness, because he would do anything to save her after discovered that she still alive.
 * Tyrant (Resident Evil): Tyrants had some weaknesses in spite of being a deadly bio-weapon:
 * Due to a prodigious increase in adrenaline over the course of mutation in their creation process, it resulting the tyrants had their hearts enlarged several times of its original size.
 * Side effect of mutation that create the Tyrants tend to reduce their intelligence, forcing Umbrella scientists to use specialized parasites to control them.
 * All produced Tyrants must wear power-limiter suits to prevent further mutation as further mutation would resulting them lose all orders that they were given, turning into a berserker-like state.
 * M. Bison: As result of expelling his own goodness from his heart to gained full mastery over Psycho Power (where the said goodness converges/become part of one of his archenemy Rose), M. Bison already doomed to become evil person for the rest of his life. Also, his tremendous powers proved too much for his body that he required some spare bodies to keep himself alive.

Comic Books

 * Carnage (Marvel): Carnage had 3 weakness, which are heat, sonic wave, and his own insanity and bloodlust that can be used against him.
 * Joker: Joker's weakness seems to be Batman and his own insanity. Connection between his insanity and the Dark Knight seemed to be apparent as due to the hero repeatedly defeat him, Joker seemed to become fascinated to the dark knight that he not taking a truly serious attempt to killed him in spite of capable to try to break him through harmed those whom he cared about. Also the said insanity seemed to made him unable to/hindered his capability in feeling love: Some of his incarnations shown truly love his partner Harley Quinn and other prefer to abuse her instead.
 * Electro: Electro would weakened by water due to electricity-based powers, but eventually learned to counteract it by using electromagnetic field that would disperse water into steam before hitting his body.

Literature

 * Captain Hook: he's afraid of the crocodile since the reptile eat one of his hand in the middle of fight against Peter Pan.
 * Lord Voldemort: As confirmed in Harry Potter and the Half-Blood Prince, Voldemort had 2 weakness:
 * Incapability to understand love and kindness: Since he unable to perceive love, he tend to having himself facing obstacles that very hard to overcome such as those who willingly to sacrifice their lives to protect Harry or their relatives.
 * His Horcruxes: Because he transferred pieces of his soul that shredded by consequent sins from hi murders on innocent people to gained immortallity, destruction of his Horcruxes would render him mortal once more and he cannot move on to afterlife due to his mutilated soul trapped in Limbo, something that Harry discovered when he entered Limbo.
 * Agatha Trunchbull: Trunchbull revealed to afraid with superstitions and supernatural things, which resulting her suspectible to Matilda's powers.