In Atlantis: The Lost Empire, Commander Rourke, who planned to steal the crystal from Atlantis all along without telling Milo, punched the King of Atlantis, mortally wounding him given how old he is. It was enough for Dr. Sweet to turn against Rourke and try unsuccessfully to treat the King's wounds when everyone else was abandoning Milo and the people of Atlantis taking the crystallized Kida with them, even before Milo's sarcastic, fatalistic appraisal of the people he thought were his friends actually convinced Audrey, Vinny, Moliere, Cookie and Ms. Packard to join him and abandon Rourke, who had just crossed the line even further by punching Milo down for his "soapbox," and stepping on the picture of Milo and his grandfather, breaking the glass of the frame.
Steele from Balto seems to be your average animated movie Jerkass at first—making fun of Balto, flirting with Jenna even though she's not interested, etc etc. All par for the course. But when he refuses to let Balto take the crate of medicine, thus condeming the children who desperately need it to certain death, it becomes clear how horrible he is. And, once he was defeated, he deliberately tried to ensure that Balto and the whole team of dogs got lost and died, while he could return home and pretend to be a heroic survivor.
Gaston from Beauty and the Beast comes close to this when he tries to blackmail Belle into marrying him by threatening to have her father tossed in the loony bin. He comes closer to it still when, out of envy of the Beast, he breaks down and stirs the town into an angry mob to make them kill him. However, Gaston finally crosses this by literally stabbing Beast in the back after Beast spared his life (and wearing a very nastysmile while doing it). He falls to his death soon afterwards.
Callaghan from Big Hero 6 crosses this upon his Redemption Rejection. Instead of listening to Hiro, he still insists on trying to murder Krei and tearing down his entire company, along with Hiro and his team. The ending hints, however, he may not be beyond redemption.
In A Bug's Life, Hopper probably crosses the line once he kills two of his own underlings to pass his message: it's not just about the food, it's about keeping the ants in line. And it all begun because a freak accident ruined the food originally set out for the grasshoppers, making Hopper think he needed to tell them "You Have Failed Me". And thousands, if not millions, of puppies continue to be kicked afterwards, as one of his goons reveals Hopper planned to squish the Queen after they finished the mass food theft just to teach the "lesson". When this is about to happen, and after suffering a No-Holds-Barred Beatdown at one grasshopper's hands, Flik confronts Hopper with a "The Reason You Suck" Speech ("Who's the weaker species? Ants don't serve grasshoppers! It'syouwho needsus!"), but this pushes Hopper even further past the line, especially when the ants decide to stand up to the grasshoppers. In the ensuing chaos, an enraged Hopper tries to kidnap Flik, but when his attempt is foiled, this pushes Hopper so far beyond the Horizon that there is no going back, especially when Hopper confronts Flik again.
Hopper:[rough with pure hatred] YOU THINK THIS IS OVER?!?!? ALL YOUR LITTLE SCHEME DID WAS BUY THEM TIME!! Flik: No, please! Please, Hopper! Hopper:[grabbing Flik's throat] I'll get more grasshoppers and be back next season! But you won't!
Darla Dimple and her servant Max from Cats Don't Dance crossed it when they sabotaged Danny's chance to impress L.B. Mammoth (or, more specifically, their method of doing so). They do so by flooding the stage with so much water that it practically drowns the entire studio (which, if this were realistic, would have killed lots of people), but instead, it sets up Danny and co as incompetent and causes them to abandon the production, less scary and not as bad as the other examples, but still a Jerkass move.
Lady Tremaine from Cinderella is established as a nasty piece of work throughout the film, and her deliberately breaking the glass slipper at the end is particularly cruel enough to be considered a possible candidate for her MEH since she did it purely out of petty hatred toward Cinderella (and she also shows no regard for the Grand Duke's life), but she truly seals the deal in the third installment, A Twist in Time, when she poofs Cinderella in a twisted pumpkin carriage with Lucifer as its human driver, and attempts to get Lucifer to kill Cinderella (especially heinous because previously, she had been satisfied with simply making her life a living hell). She also has Anastasia posing as Cinderella to fool the prince. If anyone doesn't know, this is rape by association. As The Nostalgia Critic put it:
Nostalgia Critic: She had no magical powers, no minions, all she had was complete control over one person's life. And man, did she squeeze every last drop out of it.
Chester V from Cloudy with a Chance of Meatballs 2 crosses this by kicking Flint down a cliff to try and kill him, revealing his Evil Plan to have all the sentient food animals turned into food bars, and trying to drop Flint's friends into a machine to shred them to bits.
Lord Barkis Bittern in Corpse Bride crossed the line a long time ago after he murdered Emily in cold blood to steal her dowry.
In The Curse of the Were-Rabbit, Victor Quartermaine starts out as both Wallace's rival (whose MO is killing rabbits) and smarmy competition for Lady Tottington. But he shows his true colors when he learns that Wallace is really the Were Rabbit, and is now more determined to kill him so he can have Lady Tottington.
The Emoji Movie: A completely unintentional one. When the Just Dance app gets deleted along with Akiko Glitter and Hi-5, Gene and Jailbreak go in to rescue Hi-5..... and don't even consider trying to save Akiko, leaving her to likely be erased from existence if Alex ever empties his trash bin. What makes matters worse is that the app is only deleted because of a problem Gene caused.
Grandma Got Run Over by a Reindeer. Slimy, and sexyEnsemble Darkhorse Cousin Mel is so desperate to be rich she tampers with Grandma's fruitcake intending to poison or possibly even kill innocent strangers to stop customers from coming to their store. When that plan unexpectedly gets thwarted, she refuses to reveal that Santa Claus really did run over Grandma to make sure she stays missing, exploits Grandpa's senility to get power of attorney on the store, and later kidnaps a now amnesiac Grandma in order to frame Santa and get all his money.
Heavy Metal. During the Harry Canyon segment, the titular character helps an unnamed woman hide from a group of thugs who want the Loc-Nar from her. The following day, Ratnik, the leader, contacts Harry to meet with him at the Statue of Liberty and give the Loc-Nar to him in exchange for a huge sum of money, getting the woman out of danger. And how does the woman thank him? By pointing a gun at him and demanding the entire amount for herself. The two of them previously agreed to split it in half. Although, the film implies it wasn't entirely her fault. The Loc-Nar is said to corrupt the will of people it interacts with, and bring out the evil potential within them.
In How to Train Your Dragon 2, if it wasn't clear enough by then that Drago Bludvist is 100% morally bankrupt, it most certainly was when he uses his Alpha to brainwash Toothless into killing Stoick.
Most Disney villains are goofy, somewhat quirky people, and even Queen Grimhilde, Lady Tremaine, and Scar had a funny and/or quirky moment or two. But not Judge Claude Frollo from their version of The Hunchback of Notre Dame. If he didn't cross this after almost dropping a baby down a well, he did after burning down multiple homes with families still inside them. And he kills Quasimodo's mother within the first few minutes of the movie! That means that he crossed the line shortly after the film began and just kept running. The fact that Frollo uses religion to justify his actions only makes it worse. In the opening sequence, the music seems to indicate a crossing of the M.E.H. when he decides to kill baby Quasimodo. About five seconds after he says, "A baby?... A monster!" The music jumps keys and tempo as he moves towards the well, and is supposed to make you realize "Oh S*** he's going to kill a baby in the first five minutes of a Disney movie!", so there will be NO redemption for this guy.
In The Iron Giant, Kent Mansley crosses it when Dean tries to warn the Army to stop firing on the Giant because he has Hogarth in his hands. Mansley promises to inform the General, only to lie through his teeth and say that the Giant killed a kid, knowing damn well Hogarth will be caught in the crossfire. He later proves to also be a Dirty Coward at the climax, just to solidify it.
When Tai Lung confesses to Shifu that all he ever wanted was to make him proud, only to find out that he had Shifu's pride and love all along, he only spends one moment looking genuinely affected before he's right back to demanding the scroll, saying he doesn't care about apologies. Since he's basically thrown away any sort of redemption that might have been offered to him, that moment signals that he deserves everything that happens to him afterward.
In the second Movie, Lord Shen, as far as he appears on the screen, always was a power-hungry murderer, but he really crosses the line when he massacres an entire panda village. As if that isn't enough he coldly kills the Wolf Boss just because the Wolf Boss didn't want to murder his own men.
Legend of the Guardians: The Owls of Ga'Hoole: Kludd moonblinks his baby sister, which is essentially zombifying her. In the book, he crosses much, much sooner, although Soren/the reader doesn't know it at first. He shoves Soren out of the nest, hoping it will kill him (his own brother) then does the same to said little sister, and has a hand in his own parents' deaths.
Scar evidently crosses this by murdering his brother Mufasa. It even seems, from Scar's facial expression at the edge of the cliff, that he realized there would be no going back once he did this, yet he did it anyway. Further evil actions (such as tricking Simba into blaming himself, or sending the hyenas after him) were done to get away with murdering Mufasa, which makes that the most likely candidate for Moral Event Horizon. When Simba finally tries to use the same words against Scar that he used against Simba (to "run away and never return"), instead of complying, proceeds to engage in an epic battle with Simba. But just before Simba and Scar battle, the latter foolishly blames the hyenas for everything, effectively sealing his fate when Simba leaves him to them.
In The Missing Lynx, Newmann overly crosses the line when he chose to try again hunting on the fugitive animals repeatedly, usurps Noah's control, and threatens to kill Felix in order to use Lynxette as bait.
Randall Boggs from Monsters, Inc. plans to kidnap small children so he can use the Scream Extractor on them, a device that sucks the scream and oxygen out of them, running the very real risk of suffocating them to death. And unlike Waternoose, who crosses the Horizon himself due to this same set of circumstances, he can't claim to be a Well-Intentioned Extremist, because his reason for doing it is petty jealousy against Sulley — jealousy which, as it turns out, goes back to the prequel, where it's revealed that all this time, Randall had been beaten out as Scare Leader by a college dropout, making his jealousy all the Harsher in Hindsight.
Raccoon crosses the MEH when he leads Surly to destroy the Tree, and banished him hypocritically. He reveals his true colours to the rest of Surly's gang of rodents via trying to suppress the nut heist. Unfortunately, The Caligula got his just desserts upon getting himself surrounded by the sharks while trying to concoct an alternative plan.
Pharaoh Seti in The Prince of Egypt led a campaign to curb the Hebrew population by rounding up and killing all of their infants. He's not too sorry about it, either, with murals depicting the event adorning the walls of his palace. When Moses, his adopted son, tries to call him out on it, Seti just blows off his concerns, saying "Oh, my son... they were only slaves..." He thought this would make his adopted son feel better. He was trying to comfort him with those words.
Dr. Facilier of The Princess and the Frog has an entire plan that puts him over the line — in exchange for wealth and status, he's willing to sacrifice the souls of everyone in New Orleans to his "friends on the other side."
Likewise in its sequel, it's not that clear when McLeach, who kidnaps a young boy named Cody to try to get the location of some eagle out of him, crosses this, but it's likely towards the end when he ties Cody to a crane, lowers him into a crocodile-infested river, raises him back out again, and would dunk the boy in again until the power on his halftrack goes out. When this happens, he takes out a gun to shoot the rope, suggesting that he was originally intent on murdering Cody anyway and just wanted to torture the kid first.
Tzekel-kan shows that he is willing to act as accessory to the massacre of his own people with his attempted sacrifices and pressing requests towards the gods to let him purge the city of those that he considers sinners. Even arguing that presiding over a religious system that, while certainly unpleasant to both Miguel and Tulio's European perspective and the audience's modern-day one, would've seemed perfectly natural to a man of his time and culture, one cannot ignore that he was the only one obsessed with enacting it even when the gods denied his request, or the fact that he sacrificed his own henchman, who if anything else, should not be considered disposable, according to his beliefs. And toward the end of the film when he agrees to lead the Conquistadors to the city and allow them to pillage it, not only to spite the Chief for banishing him, but also because he sees them as the ideal gods, it becomes clear that he's genuinely evil no matter whose perspective you're coming from.
Cortez would have his expedition which would bring slavery and destruction to the so called heathens as his MEH if he didn't cross it when he planned to have Miguel and Tulio flogged and then sell them into slavery, all for accidentally stowing away on his ship.
Though for the most part he's as Laughably Evil as the average Disney villain, Prince John from Robin Hood crosses it when he plots to use Friar Tuck as bait to capture Robin Hood, knowing Robin Hood will save any friend of his who's in danger. Even Sir Hiss is shocked to hear that his boss plans to hang Friar Tuck. He further goes over when he tries to murder Maid Marian in the alternate, extended ending, which makes it all the more understandable when King Richard has his brother locked up and notes that were it not for their mother, he'd have him executed then and there.
The Grand Duke Of Owls crosses this in Rock-A-Doodle when he nearly strangles Edmund to death.
Then, it only went downhill when she and Jean-Claude cross this when they're willing to lock children away in a warehouse for the sake of a perfect wedding.
Jean-Claude pilots the Super Escargot mecha against the babies' Reptar mecha and attempts to destroy it, knowing full-well the babies are inside and even gleefully going along with it.
Sausage Party: Douche crosses it when he kills an injured juice box.
Eris of Sinbad: Legend of the Seven Seas crossed this when she unsatiably took matters into her own hands upon framing the titular protagonist by stealing the Book of Peace. She pushed even further when sending her pet Ice Eagle, Roc to attack Sinbad and his Crew
Snow White and the Seven Dwarfs. After Snow White has grown up enough for the mirror to declare her more beautiful than the queen, the queen orders her hunter to kill her and bring back her heart as a trophy (she even already had a box custom-made for the occasion). When that doesn't work, it turns out she's studied murder spells as a backup plan. When she learns that the Sleeping Death spell she's put on a certain apple will only leave Snow asleep and can be cured, she isn't fazed but rather delighted — because she's sure that the dwarfs will bury Snow alive! Snow must have had her hands full as the new Queen — she probably had to sort out some pretty sadistic lawbooks.
Superman in Superman vs. the Elite jumps through the MEH when he decides to finally buy what Manchester Black is selling... by murdering each of the Elite, then lobotomizing Black by destroying his powers. Then, we find out he subverted it by revealing none of the Elite are dead, that an army of robots saved them, and that his way works.
Clayton from Tarzan crosses this when he shoots Kerchak, Tarzan's adoptive father, then, much like Gaston, tries to kill Tarzan after Tarzan spares him, resulting in a gruesome Karmic Death afterward.
Mother Gothel in Tangled officially crosses the line either
When she stabs Flynn Rider and very nearly kills him, so that Rapunzel's secret would die with him.
Or arguably even before already when she sets him up to be caught by the authorities knowing that he will be sentenced to death, which nearly happens, but he escapes that, only to be stabbed by Gothel as mentioned above.
Lotso had already established himself as a dog-kicking machine as he tortures and corrupts the toys during the movie, but irrevocably crosses the horizon in Toy Story 3 when he refuses to help Andy's toys survive the incinerator after they went out of their way to save his behind moments earlier. He even mocks them with the remark "where's your kid now, sheriff?", complete with a mocking salute and evil smile. As a result, his Laser-Guided Karma of being trapped in a truck is well-deserved.
More than half of the short animated film Zero in one long crossing of the horizon for everyone at the expense of the title character who happened to be born with number zero on his chest. He is continuously abused and physically assaulted and they almost murder his pregnant wife in front of him after imprisoning him. It is clearly shown that this happens to all zeroes and it is a film about the horrors of racism, casteism and social unequality.
Zootopia: Bellwether crosses it when she shoots Nick with the Nighthowler serum (which he thankfully switched out prior with blueberries) in an attempt to make him kill Judy. Considering how friendly and supportive Bellwether had been to Judy in all their previous encounters, it really drives home how twisted the little sheep really is and how far she'll go to get what she wants. Bonus points for her choosing to simply stand there and watch Judy be hunted and killed, even giving a Psychotic Smirk when Nick clamps down on her neck. And that's not even going into her whole scheme, which involved transforming innocent citizens into mindless, savage beasts without any concern about their loved ones or the possible casualties and planned to use them to turn the whole city against predators.
In The Powerpuff Girls, if you thought that Mojo Jojo was an incompetent and harmless villain in the TV series, be disappointed when you see The Movie. He arguably crossed it by enslaving Townsville with super monkeys, destroying half the town, and betraying the girls' trust in the process. Confronted with this development, he tries to Break Them by Talking: