Complete Monster/Teenage Mutant Ninja Turtles

Yes, the heroes in a half-shell have faced plenty of villains without even a half-heart.

1987

 * The original cartoon gives us Lord Dregg, the replacement of Shredder and Krang. He is portrayed much more nefariously and seriously than either of those two. To start, he frames the Turtles for all manner of heinous deeds in the city and claims he is humanity's savior, only to begin unleashing his minions throughout the city, causing mass devastation. Dregg hires a mad supervillain named Chronos to trigger earthquakes throughout the city, and constructing a death ray to level cities until the rest of the world bowed to him. His true motives and cowardice are revealed by the arrival of Doomquest. In the season 10 premiere, he jettisons his loyal minion Hi-Tech into space to die for his failure, despite his loyalty, and in yet another episode, we see what would happen if he won; a world were people are Released to Elsewhere en masse, infested with horrible pollution. Within the tenth season, he plots to turn Leo into a walking nuclear bomb, teleporting pieces of the sun to Earth, taking over defense satellites to fire them at the planet, and taking the planet through a wormhole to a galaxy where he had already won. He eventually loses motivation to rule the world insofar as to simply leave the Turtles stone-cold dead. In the series finale, not only does he absorb 5 powerful mercenary aliens to consume their powers, he abandons his other loyal flunky, Mung, who raves that he is mad. Is it any surprise he's one of the few classic TMNT nasties to die permanently?

2003

 * Ch'rell from the 2003 Teenage Mutant Ninja Turtles series was an Utrom criminal who was imprisoned by his people for his various crimes. Ch'rell managed to force the transport ship he was being carried on to crash on Earth. Ch'rell escaped and took the guise of an Japanese crime boss named Oroku Saki, better known as the Shredder. Wanting revenge on his people, the Utrom Shredder went to great lengths to find the Utroms still marooned on Earth.
 * In the series, Shredder attacked Splinter's master, Hamato Yoshi, believing he worked for the Utroms. After having his minions work over Yoshi with torture, Shredder personally killed Yoshi,an act that would lead to Shredder becoming the Turtles' Arch Enemy . Shredder's Foot Ninja also kidnapped innocent people and mutated them into monsters to use as slave labor to try a locate a possible Utrom base underground. Shredder has shown to be a very cruel boss. He murders one of his men who failed to deliver some stolen goods for him, due to the Turtles involvement. Shredder also would punish Baxter Stockman for his failures, by grievously injuring him, until eventually Stockman was nothing more then a Brain in a Jar. Shredder also displayed a complete disregard for human life, after an Triceraton Invasion resulted in Beijing becoming a city floating in the sky, Shredder decides to steal the anti gravity generator that is keeping the city in the air. When Karai objects noting that stealing the generator will result in the city crashing into the ground and killing millions in the process, Shredder overrules her and tells her to do it anyway. Some of Shredder's worst crime happen when Donatello visits a Bad Future where Shredder is a dictator who controls the world. Shredder has Secret Police on the streets to round up any dissenters and is using both Utrom and human slave labor (with humans having to work 18 hours a day) to build a giant teleportation device, so Shredder can conquer other planets. In this future, Shredder executes his former servant Hun, while Hun is begging to be let back into his service.
 * Ch'rell returned in the movie Turtles Forever. After being rescued from imprisonment by 1987 Shredder and Krang, Utrom Shredder takes over their Technodrome and uses its technology to try and conquer The Multiverse. When Shredder discovered that the Teenage Mutant Ninja Turtles are in every alternative reality, he starts to lose it. Shredder decides to find the Prime Universe and kill the Turtles in that reality, which he believes will destroy the rest the multiverse. When Shredder discovers that he too will be destroyed along with the rest of the multiverse, Shredder still doesn't care, putting his hatred of the Turtles and desire for revenge above everything.
 * Tengu Shredder, the man Utrom Shredder took his identity from, started off as a man named Oroku Saki in 3rd century Japan. A giant Tengu demon was rampaging across the land and the Emperor sent Saki and 4 other champions to destroy it. Saki seemed to have killed the demon, but really made a deal with it, allowing the demon's spirit to enter his body, selling his soul in exchange for power. Saki began to call himself the Shredder and went on a rampage, trying to conquer Japan. The other 4 champions begin to study magic and then confront the Shredder. They manage to defeat Tengu Shredder and seal him away. However in the 21st century Tengu Shredder's minions manage to free him. Rather then being grateful, Tengu Shredder tortures these minions whenever they annoy him. Tengu Shredder decides to kill Karai, who has taken the mantel of the Shredder, believing that to be an insult. Tengu Shredder causes random destruction on the way to Karai's tower, endangering random citizens. Tengu Shredder decides to play mind games with Karai, taking the form of the Utrom Shredder to mock her and then stabs her. Karai survives, but Tengu Shredder moves on to his end game, he goes to city hall and transforms it into his personal palace. He then transforms New York into a nightmarish hellscape where demons and the undead attack the citizenry, Tengu Shredder intends to transform the rest of the world in a similar fashion.

2012

 * Dr. Victor Falco, AKA the Rat King. The Turtles meet him while investigating a scientist's mysterious disappearance, and while Falco at first seems like a decent guy, it's soon revealed that he kidnapped his colleague in order to mercilessly perform torturous experiments on him that mutate him into an ape-like creature so that he can use the mutated DNA to create a serum to gives himself Psychic Powers. While moderately successful at this, Falco ends up losing his job and having to continue his experiments on rats in private. A freak accident leaves him blind and disfigured, but also grants him the psychic ability to control rats. Claiming to be in touch with the rats' views, Falco turns against humanity for being "filthy vermin", adopts the name Rat King, and seeks to have his rats take over the city by driving the humans away. He also ruthlessly Mind Rapes Splinter several times to break his spirit and turn him into his slave. He goes as far as to manipulate Splinter with memories of his dead wife and daughter, and then uses him as a weapon to destroy his own sons! He later returns again, kidnaps several civilians, including teenagers, and plans to experiment on them to turn them into hybrid "rat people". While his first attempt results in a deformed creature that is immobile and in constant pain,it does nothing to deter him from his experiments. He unleashes a hoard of rat monsters onto the city to attack and kill several innocents, taking sadistic glee in it the whole while. And then he assaults Splinter's mind to get him to destroy his sons again. And despite his supposed kinship with his rats, he has no problem using them as test subjects and disposable sacrifices. With that said, not even the Shredder is as vile and monstrous as the Rat King in this series.
 * The primary villain of the first three seasons of the 2012 series, Kraang Prime, is a grotesquely large, demented Utrom warlord who fancies himself a god. Developing psychic powers from mutagen, he brainwashed millions of innocent Utroms, crafting an army of servile "Kraang" to invade and destroy planets, ultimately setting his sights on Earth as his petri dish. Spending millennia killing and torturing humans to create a new Dimension X, he then decides to turn the massive metropolis of New York into a mutant colony, succeeding and transporting millions of victims to Dimension X as slaves. After that, his scope expanded to the entire planet, with him loading a missile with mutagen as a last resort. Relentless, cruel, and deceitful, Kraang Prime was a massive threat to the Turtles and all Mutantkind.
 * Kavaxas in Tales of the Teenage Mutant Ninja Turtles is the draconic ruler of the Netherworld who desires to bring about the apocalypse. After he's summoned by Tiger Claw, Kavaxas is forced to work alongside him and the Foot clan so they can resurrect the Shredder and defeat the Turtles and their friends. After Kavaxas brings Rahzar back to life as one of his minions, he goes after Hattori Tatsu and kills him before stealing Shredder's helmet. He later attacks Don Vizioso's gang and kills some of his mobsters before stealing the Shredder's heart, all while repeatedly trying to kill the Turtles. With both items in his possession, Kavaxas successfully resurrects the Shredder before betraying Tiger Claw and the Foot clan; Kavaxas proceeds to unleash thousands of spirits onto New York as he attempts to cause The End of the World as We Know It.

2019

 * Batman vs. The Teenage Mutant Ninja Turtles, based on the comic book series of similiar name, has these three examples.
 * The Shredder, the leader of the Foot Clan, aligns himself with Ra's Al-Ghul in order to obtain immortality from the Lazarus Pit by agreeing to build a machine that could spread the mutagen across Gotham City, invading various corporations and killing the staff who happened to be there and stealing technology. The Shredder was able to nearly complete the machine, only failing to acquire the Cloud Seeder when Batman intervenes, in which the Shredder beats him half to death before fleeing. Changing their plans, the Shredder breaks into Arkham Asylum with Ra's and murders all the security guards and breaks all the inmates out, but not before obtaining Joker's Joker Venom and giving him the mutagen to mutate the inmates and distract Batman and the Turtles. After Ra's hired The Penguin to successfully steal the Cloud Seeder, the Shredder kills all of Penguin's henchmen and threatening to kill him as well when he demanded a payment. The Shredder reveals that after he obtains immortality, he will kill Ra's Al-Ghul and take over the League of Assassins, then use the Joker Venom/Mutagen hybrid, which mutates people into psychotic violent mutants, himself.
 * Ra's Al-Ghul, the leader of the League of Assassins, lacks his redeeming qualities as a Well-Intentioned Extremist that cares for his family from the comics in favor of being a ruthless madman obsessed with chaos and conquest, even showing how little he cares about his allies; he sacrifices one to be mutated by the mutagen, stating that he has plenty more if he died from the effects. Making a deal with the Shredder for his mutagen and to build the aforementioned machine in exchange for the Lazarus Pit, Ra's over the time becomes less faithful and impressed by his partner's efforts and creates a back-up plan in which they give the Joker the mutagen to mutate the inmates of Arkham Asylum to use as a distraction for Batman and the Turtles while they work on the machine. Ra's combines the mutagen with Joker Venom to create a psychotropic variation of the mutagen that not only mutates people but turns them violent and homicidal, and wishes to spray this over Gotham City to create chaos and destruction and wishes to repeat the process across the world and bathe it in blood and fire.
 * The Joker, the psychopathic Clown Prince of Crime, is released from his prison by Ra's Al-Ghul and the Shredder and is given the mutagen in exchange for his Joker Venom formula. The Joker then uses the mutagen to mutate all of the inmates in order to distract Batman and the Turtles while Ra's and the Shredder complete their plans. These events led to Leonardo being psychologically torture by the Scarecrow with his Fear Toxin and injecting Batman with the Mutagen/Joker Venom hybrid leading to him become a psychotic version of Man-Bat and almost kills his allies, including his son Damien. While an Arc Villain in comparison to the two Big Bads of the film, Joker still proves he's a depraved and sadistic psychopath.

Comics

 * Mirage Comics:
 * While the original comics were already very dark in nature, the Arc Villain Bloodsucker stands out as a truly repulsive creature. A leech who sucked Raphael's mutagen and became an anthropomorphic being, Bloodsucker decides to attack the innocent in search of blood. Feasting off of a park ranger, he then goes after innocent children. When the Turtles arrive to save them, he flings a tree at them, saying that he specifically enjoys human blood, and when the turtles drown, he will feast on each of their dead bodies. His chilling remarks to his next victim only accentuate the threat of the creature, as he dreams of turning the whole human race into his personal ranch, hunting down every one of them to feast on their blood. While revealed to work under another villain, this doesn't soften his chilling deeds at all. While most antagonists in Mirage were Anti-Villains or comical stooges, Bloodsucker is a sharp contrast to this.
 * Despite being just a Filler Villain, Skonk manages to come across as one of the most vile street level villains the Mirage Turtles have faced. Skonk is the leader of a far-right militia who felt that, because the Cold War didn't result in a nuclear war and his militia would not be able to prove their survival skills after such a event, he would try to start a nuclear war by setting off a nuke at a critical military facility. He and his militia kidnap a nuclear physics student from the University of Massachusetts and force him to create a crude nuclear bomb. The student escapes and bumps into the Turtles, warning them of the danger. Skonk kills the student with his sniper rifle. Thinking the Turtles are just people in costumes, Skonk orders his militia to kill all of them, not wanting there to be any witnesses to his plans. The Turtles easily defeat his militia underlings, so Skonk decides to return to his base and set off the nuke right away. When Splinter and Turtles try to reason with Skonk, saying he will kill countless people with his bomb, Skonk says he doesn't care, saying there are no innocents and everyone is guilty of allowing America to fall from greatness.
 * By far the nastiest recurring foe of the Turtles in the original comics is Savanti Romero. Becoming envious of his master Lord Simultaneous, he attempts to erase him from the very timestream. Transformed into a goat demon and warped to the 13th century AD, he conquers a village and makes it into his personal fiefdom. When Renet arrives to stop him, he steals her time scepter. Creating an undead army to quash the resisting villagers, Simultaneous has to interfere himself and banish him to the Cretaceous. Unfortunately, this simply led to Savanti Romero freely causing misery across the timestream, including trying to sacrifice Renet to trigger a spell to make the meteor that killed the dinosaurs miss and ensure humanity never evolved, attempting to rip out her spine in order to gain her powers, wiping out feudal Japanese clans so that their descendants never existed, and trying to transform himself into a trans-dimensional god using the Aga-Moo-Tou, and recreate the world in his own image.
 * Serial Killer Johnny Lee Raeburn, from Savage Dragon, appears in volume 3 of this series under his moniker of "Deathwatch". Raeburn returns to Earth as a cybernetic supervillain able to feast on the minds of his victims and make them experience the terror of those he's killed, making them die in absolute fear. Deathwatch slaughters several people connected to the trial that convicted him as a child killer before single-handedly massacring his entire hometown and killing his mother, even mentally torturing Donatello into brain death before he's foiled.
 * Another terrifying one-off villain is Master Traquer from the May 1990 issue. A cruel vampire missing the days when vampires ruled the earth and indiscriminately killed humanity, he decides to kill innocent people, turning them into zombified slaves. Ordering them and his gang to track down various ancient artifacts around the world, he plans to awaken Dagon, an evil deity, who will cause death and destruction across the entire planet so vampires reign supreme again. When informed that Dagon may very well wipe out all vampires, he flat-out states that he doesn't care.
 * Archie Comics
 * Krang in the Adventures of the Teenage Mutant Ninja Turtles comic is a far crueler being than his better-known counterpart. His depths of brutality are first gleaned from Wingnut and Screwloose, who had their home planet, Huanu, genocided by Krang's forces. This genocide is in fact quite regular to Krang, who has done this to many planets in his quest to find the Turnstone. When Krang decides he needs stronger allies, he sends Maligna and her insect warriors to kill the people of Earth, colonizing it. After escaping his prison planet of Morbus, he uses Shredder as his new host to try to kill the Turtles and all whom they love, without a sense of remorse for what happens to Shredder.
 * Queen Maligna is the brutal leader of the Malignoids, alien insect warriors. She seeks nothing short of consuming countless worlds teeming with life. Sending eggs to earth that hatch into larva devouring everything in their path, she then sends adult Malignoids to attack. She has a habit of feasting upon her own children, devouring them even when they have successfully done their task. Capturing Raphael, he and Mondo Gecko were to be fattened and dipped in honey for her to later feast upon. Sending her space armada to kill the entire population of Earth, Maligna is defeated and vows to leave the Earth, but returns after Mr. Null kills the Mutanimals to finish what she started.
 * Mr. Null was introduced as an unseen tycoon, who enslaved a remote South American tribe to work in some of his mines and tries to dump toxic waste into the ocean. However, we soon discover that Null is actually a demon and has sold the Earth to the abovementioned Queen Maligna and her hordes of insectoid aliens, who plan to destroy humanity and colonize Earth. After the Turtles and their allies the Mighty Mutanimals thwart this alien invasion, Null seeks revenge on them. Null takes control of the Horsemen of the Apocalypse and captures the two groups. Null is planning to make the female members of the Mutanimals into his harem, while the others will be slowly electrocuted to death. Null plans to force Kid Terra, one of Null's former underlings who turned against him, into pulling the switch that electrocutes his enemies, wanting to torment his former employee. After this scheme is thwarted, Null later returns and hires some cyborg assassins, who manage to kill most of the Mutanimals. Null decides to torment Candy Fine, who the girlfriend of Mutanimal Mondo Gecko, by showing her images of the Mutanimals burning in Hell. Null then Mind Controls her and makes her into his slave. Null had the Mutanimals killed so he can continue what he started, trying to help Maligna destroy the human race. When asked why he does what he does, he responds thusly: "Because death, destruction, these are my favorite things, the things I do best."

Film

 * In the original 1990s films, the truly chilling Shredder would qualify. Brutally murdering Hamato Yoshi and Tang Shen due to the latter denying her love to him, he sets up an organization that lures in lonely, impressionable teenagers into becoming his evil ninja accomplices, to spark a massive wave of crime. He often has these recruits brutally killed for failure, and his reference to Splinter as a "thing" shows how inconsiderate he is. His last resort involves downing his own mutagen to be come the horrible Super Shredder to try and kill the Turtles. What sells him is his terrifying depiction in battle, with all characters who don't work for him being scared shitless of him and/or despising him.
 * 2014 film: Eric Sachs is a ruthless businessman and secretly a member of the Foot Clan. Having murdered April's father via burning down his lab, his true plan is to use mutagen to spread a mass epidemic and then cure it to get rich. In order to regain his lost mutagen, he painfully drains the Turtles of their blood, infecting one of his own soldiers with the toxin to demonstrate how it works.
 * The Shredder himself is the true leader of the Foot Clan, who have been terrorizing New York for many years. With a bodycount of at least 32, he plans to infect the city with a flesh-eating toxin, and once the Turtles destroy the mechanism, he begins to throw it down manually. In the next film, he sells out the earth to dangerous alien warlord Krang by building a teleportation device for him.