Teenage Mutant Ninja Turtles
Moral Event Horizon in this series.
Leonardo: You killed him! He was your brother, and you killed him! (Between exchanged blows) He was your brother, Saki! Your best friend! How could you do that?!
Shredder: Splinter was cursed to become a loathsome rat! It was his fate... HIS DESTINY!
Leonardo: You're a monster! A demon! Is that YOUR destiny?
Teenage Mutant Ninja Turtles (1987)
- In the season 8 premiere, Shredder actually destroys the Channel 6 building to spite the Turtles, which takes it out of commission for the rest of the series and also leads to Burne Thompson launching an anti-Turtles campaign for the first half of the season.
- Long before that, there was Shredder intentionally exposing April to the lethal fumes of the Doku plant back in "Enter: The Fly," which very nearly killed her. And this was back in the second season, which had already been made Lighter and Softer than season 1!
- In the same episode, he betrays Baxter Stockman by sending him through a portal to Dimension X where he would be seemingly be disintegrated, only to transform into a mutant fly since a fly followed him through the portal and got into the disintegration chamber with him.
- And let's not forget the Season 5 episode "My Brother, The Bad Guy" where Shredder attempts to murder his own brother, Lt. Kazuo Saki, by handcuffing him to a drain pipe and sending the Technodrome through a portal from Dimension to towards him, which would have crushed him to death if it weren't for the Turtles' intervention.
- In the Season 3 episode "Michelangelo's Birthday", in an attempt to lure the other Turtles into a trap, Shredder, along with Bebop and Rocksteady, capture Michelangelo and attempt to kill him by strapping him to the Flushomatic and spill acid over him, on his own birthday, no less!
- It could be said that Shredder crossed it long before the events of the series when he got Hamato Yoshi expelled from the Foot Clan by pinning the back of the latter's kimono to the wall with a knife, leading the visiting sensei and students to accuse Yoshi of plotting to assassinating the sensei, and subsequently turning the Foot Clan into a criminal empire.
- In "Shredder Triumphant", Bebop and Rocksteady try and shove the Channel 6 crew out of a window.
- In "Return of the Technodrome", Krang tries to destroy New York with an earthquake after its populace refuses to vacate the city so he can use it as a base of operations.
- In the first-aforementioned ep, it is stated by Drakus AKA Bezerko that Krang blew up Drakus's home planet, killing his family, because he had no further use for him and wanted to prevent his family from trying to get revenge.
Teenage Mutant Ninja Turtles (2003)
- Shredder's personal Moral Event Horizon comes in the episode "Mission of Gravity", when he orders his lieutenants to steal the Triceraton engine holding the city of Beijing aloft miles above the earth, despite the fact that doing so would naturally doom the millions trapped within it. It was possible to remove the engine without killing anyone, but he didn't care.
- When Leonardo saves Karai from falling to her death, she stabs him from behind with his own katana when he would have let her go in the spaceship anyway. This is one of the things that leads him to tell her she is just as bad as the Shredder. It can be argued that every decent thing she did after that was just self-preservation.
- Technically in that instance, Shredder punched him into the blade, which Karai held at that moment. If you look at it for a split second she's visibly shocked by what just happened. So in that case it's TECHNICALLY an accident.
- Karai's alternate future self from "Same As It Never Was" aided Shredder and served him as his right-hand, even when Shredder took over the entire planet, turning it into a massive hellhole, enslaved humans and Utroms, planned to invade other worlds and reduced much of Earth's population and killed everyone who opposed him in brutal ways. Yet she still aided him and never even expressed any remorse for any of this, while stating that she just follows her duties, but at this point this argument to defend herself is meaningless. She is just as accountable for this as the Shredder. Karai from present at least questioned his acts and even went against him in "Mission Of Gravity" and pulled a Heel–Face Turn during the Turtles Forever, when she found out that Shredder was attempting to erase the entire multiverse.
- In Turtles Forever, 2003!Shredder callously attempts to murder the Turtles by using them to pinpoint Turtle Prime. Granted, he's tried to kill them hundreds of times before... but not while Splinter was watching them die, yes, the other Shredders have attempted this, but there was no real sign of a Deus ex Machina, Chekhov's Gun, or really anything this time that could save them except somebody from the outside, this is what gets Karai to finally switch sides for good.
Teenage Mutant Ninja Turtles (2012)
- Shredder crossed this when he killed Hamato Yoshi's (this was before he was mutated and started calling himself Splinter) wife, burned his house down, and took Yoshi's daughter Miwa to raise as his own, naming her Karai (meaning "weapon"), blaming Yoshi for murdering her mother, and making Karai hate her biological father. Why did he do all this? It’s essentially because he was jealous of Yoshi and he just kept going.
- Near the end of the first season, he allies himself with the Kraang, making a deal with them that would result in everyone on the Earth dead or mutated, just so he could get Splinter out in the open. Then it's revealed that Shredder didn't kill Splinter's daughter, Miwa, he kidnapped her and raised her as his own - Karai. Meanwhile, he fed Karai a lie that Splinter killed her mother, giving her a vendetta against Splinter as well. He's been using her as a pawn for revenge her ENTIRE LIFE, and she doesn't have a clue. And he doesn't hesitate to sic her on Splinter when she comes to help Shredder.
- What makes this even worse is that he's outright shown he has no compassion at all for Karai. She's simply a means to an end. Even the fact she genuinely loves him means nothing so long as he can use her to hurt Splinter. The big crossing in this regard comes when he responds to her asking if Splinter is her real father by saying yes and having her locked up. No show of sorrow or upset. No feelings of remorse. He just basically tells her 'yes, I used you as a living tool of revenge' and discards her.
- Him blaming Splinter for Karai's mutation probably counts as a better example, but for different reasons. Her mutation was more or less entirely his own fault, with Splinter having nothing to do with it. In a way, Shredder actually caring about Karai makes it worse because instead of going My God, What Have I Done?, he uses it as more fuel for his hunger for revenge instead of accepting responsibility for his actions.
- But the moment he most certainly crossed the horizon for good was in "Annihilation Earth". Shredder throws away a chance to save the world AND Karai in favor of killing Splinter through a literal, figurative, and possibly symbolic backstab, which leads directly to the Triceratons sucking Earth into a black hole.
- The aformentioned Triceratons, or to be more specific, Captain Mozar would've crossed it by by having the Earth destroyed. If this doesn't wasn't enough, he crossed it in the final episode of the Space arc in Season 4 who upon learning on his victory in one timeline, takes much more sadistic relish in his attempt to destroy the Earth a second time.
- Emperor Zanmoran crossed it for similar reasons for using the Blackhole Generator, the very device that the Kraang used to destroy his planet and most of his kind, for the same reasons to destroy the Kraang's base and kill all innocent life within Earth like any Kraang would use the device which caused Zeno to protest. Such protests would make Zanmoran definitely cross it by having him imprisoned with many other prisoners and forces him to fight other warriors to the death for his own amusement.
- If siccing a mind controlled Splinter after giving intense psychological torture to kill the Turtles who he knows are their sons wasn't enough, Rat King crossed the line by using his so-called rat brothers as pawns in capturing humans and sacrificing many of them to save his skin.
- In "Trans-Dimensional Turtles", 1987!Krang (if he didn't do so in his original series) crosses it by setting bombs in 2012!Earth, 1987!Earth, and Mirage!Earth to get rid of the Turtles forever, even going as far as to dupe his "cousin", Kraang Sub-Prime, that he was helping them conquer their worlds. Subprime did NOT take Krang being revealed to be intending to destroy the exact kind of dimensions Kraang Prime and company have spent eons trying to mutate very well.
- Lord Dregg shows how utterly irredeemable he is in the fittingly-named "The Evil of Dregg". Having his armada ready to attack the Salamndrain homeworld, he forced Mona Lisa and Sal Commander to betray the Turtles by luring them into a trap. He then reveals to the two he had no intention of sparing their planet, having plotted on eating them the entire time.
- Za-Naron crossed it when she temporarily kills Donatello while possessing April's body, in her quest to wipe out all life on Earth.
- Jei first crossed it offscreen by murdering an innocent family. Then, it's revealed that he wants to use Kintaro's body as a vessel for his spirit.
Live-action films
- Teenage Mutant Ninja Turtles (1990):
- Fifteen years before the movie began, Oroku Saki, who would later become Shredder, took vengeance upon Hamato Yoshi and Tang Shen for leaving Japan for America by first murdering Shen and then Yoshi when he came across her. When Splinter, who was just a normal rat at the time, attacked him, he threw him to the floor and sliced his ear with his katana.
- Tatsu from the same movie gets his when he beats his own subordinates in a violent rage after the junk shop battle, culminating in him savagely beating a poor Foot named Shinsho to within an inch of his life for begging him to stop this—and in the novelization and the original script, Shinsho doesn't survive. It is this scene which convinces Danny that he can't stay with the Foot any longer.
- Teenage Mutant Ninja Turtles (2014): Years ago Eric Sacks killed April's father, who had set fire to the Project Renaissance lab to prevent the Shredder from using it towards his own means.
Teenage Mutant Ninja Turtles (IDW)
- Dumber-than-a-sack-of-hammers they may be, Bebop and Rocksteady hit this when they nearly killed Donatello, Bebop holding down the turtle while Rocksteady smashed his back with a sledgehammer.
- Bishop doesn't cross the Moral Event Horizon so much as he kicks it in the ass and spits on it after he kills his own father, a defenseless elderly man, with zero hesitation.
- He gets a second one when he brainwashed Slash and implanted a nuclear bomb in him, forcing the poor thing to self-terminate.
Teenage Mutant Ninja Turtles: Mutant Mayhem
- Cynthia Utrom crosses it when she has the turtles "milked" for the mutagen in their blood.
- Superfly crosses it when he moves forward with his plan to have all of humanity mutated; even when the turtles were able to convince the other mutants not to go along with it.
