In some games, the main villain is able to broadcast messages to the hero over the course of the game, and they'll eventually lose it and start broadcasting more and more desperate pleas/insults/bribes to you as you get closer to them.
BioShock does this with both Andrew Ryan ("Does your master hear me? Atlas! You can kill me, but you will never have my city!") and Frank Fontaine ("I'm gonna splice, and splice, until THERE'S NOTHING LEFT TO SPLICE WITH!!").
In BioShock 2, Sofia Lamb spends most of the game smugly lecturing the player on her superior ethics. By the end she's a bitter, broken woman, knowing that her own daughter has rejected her and her plan.
BioShock's spiritual predecessor System Shock has something similar in the second game after the final boss fight, where SHODAN goes from taunting and mocking the player to attempting in vain to bargain for her life.
Dr. Breen in Half-Life 2 ("Look, Gordon, look at what you are throwing away. Is it worth it?").
Another (albeit somewhat milder) Half-Life 2 example: In Episode One, the Vortigaunts manage to break through the G-Man's power and rescue Gordon, which somewhat intimidates the G-Man in response. ("We'll see... about THAT!")
GLaDOS in Portal ("Turn back now or I will kill you! ...I'm going to kill you. And all the cake is gone. You don't even care, do you!?").
"Stop squirming and die like an adult or I'm going to delete your backup. STOP! Okay enough, I deleted it. No matter what happens now, you're DEAD. You're still shuffling around a little but believe me you're dead. The part of you that could have survived indefinitely is gone. I just struck you from the permanent record. Your entire life has been a mathematical error. A mathematical error I'M ABOUT TO CORRECT."
Wheatley in Portal 2, as you get closer to his lair and his traps fail again and again. The pinnacle is in the Final Battle after Chell (barely) survives yet another trap. ("What, are you still alive? You are joking! You Have Got to Be Kidding Me! Well, I'm still in control. AND I HAVE NO IDEA HOW TO FIX THIS PLACE. Oh, you had to play bloody cat and mouse, didn't you? While people were trying to work. Yes, well, now we're all going to pay the price, BECAUSE WE ARE ALL GOING TO BLOODY DIE! Oh, brilliant, yeah.")
Bob Page in Deus Ex's final mission. ("Go ahead! Blow this place sky-high... You might get rid of ME, but you'll take down Aquinas, the power grid, the whole electronic infrastructure. Is that what you want? Are you completely nuts?")
It gets better. He goes from smugly taunting you to begging.
Merely suggesting that Helios will join with someone other than Page sends him into a raging fury, which is a stark contrast to how he was taunting you just a moment before you speak with Helios.
Nicole Horne in Max Payne ("What do you mean, 'he's unstoppable'?")
The deity in Tower Of Heaven ("How dare you... How dare you continue to live? Is it merely to spite me?")
By the end of Halo 3, the Gravemind has gone from calmly taunting the Master Chief with visions of Cortana and statements of his complete inability to stop the inevitable to rampant screams and roars of protest — though it kind of makes sense, as the Chief is about to fire Halo right in his face.
Even then, when the Flood are about to be eradicated, Gravemind suggests that all the Chief will succeed in is delaying the inevitable.
Gravy's breakdown actually starts in the previous level. He taunts the Chief as you move through a extremely Flood-infested High Charity, then goes to threats, then to demanding that you die, then to outright enraged yelling.
The Prophet of Truth also goes through this. As the humans and Elites (who are now working together) get closer and closer to beating him (having annihilated his forces over the course of the game) his preachings as the Chief and the Arbiter come closer and closer to his location get less religious and "ascending to godhood" to more "THIS IS ALL THE HERETICS' FAULT!!!". His last words are "I...AM...TRUTH! THE VOICE OF THE COVENANT!" after he's finally cornered with the Covenant completely destroyed and the Chief shuts down the Halo rings.
Neither Gravemind or Truth can compete for the "honor" of "The Best Villainous Breakdown of the Halo series" when facing 343 Guilty Spark. While both Gravemind and Truth started yelling around, they didn't do anything physically toward the player. Spark however starts shooting lasers from his red, formerly blue, eye at the player and messing up his power-armour, while screaming "UNACCEPTABLE! UNACCEPTABLE!! ABSOLUTELY UNACCEPTABLE!!!" or "THIS RING BELONGS TO ME!!". And he kills Sergeant Major Johnson in his fit of rage.
And of all places — KirbySuper Star, as Kirby's systematic demolition of the Halberd is accompanied by running commentary from Meta Knight and his crew, with increasing alarm.
Not an entire game, but during Chapter 2 of Paper Mario, this happens with Tutankoopa as you progress further and further through the Dry Dry Ruins.
Subverted in Chapter 5 of Paper Mario: The Thousand Year Door; most of the dungeon has you hearing moaning messages from Cortez in the same vein as those of Tutankoopa (complete with a gradual breakdown), but when you arrive at Cortez's chamber, he says that he's sick of putting up that ruse, since "Pirates don't moan!", and starts showing his real personality - which is about what you would expect from a pirate king and hasn't been broken down at all.
In Borderlands 2, Handsome Jack has a pretty big one as his last monologue. Now, while his breakdown did start when you kill Angel, who is his daughter, his last desperate, hoarse rant at how he's the big hero and the Vault Hunters are bandit scum in the aftermath of his whole plan falling to pieces at the last moment is definitely the climax.
In the Sir Hammerlock's Big Game Hunt DLC, Professor Nakayama's breakdown starts more or less as soon as he successfully goads the Vault Hunters into coming after him (if only just to shut him up). He then spends the rest of the DLC in utter fear of the players and freaking out as they carve their way through his forces.
Arcturus Mengsk in Starcraft II after Raynor broadcasts his controversial recordings to the Dominion
Mengsk: YOU jackals think you can come here and question ME?
Kerrigan also suffers this during the final battle. In the beginning she's smugly taunting them, but as Terrans continue to hold off the Zerg, drive her back, and the artifact increasingly gains power she starts to scream angrily.
None of them broke down quite as spectacularly as Von Karma. Especially when you get to rub in his face the fact that he never would have been caught for the original DL-6 murder if he hadn't been obsessed with getting revenge on Edgeworth by manipulating Yanni Yogi into the present day murder, therefore drawing attention to the original case and allowing Phoenix to solve it. Oh, and it's hard not to enjoy watching him ram his head into the wall.
Truly, the most spectacular breakdown is Damon Gant's. No one else's breakdown involves their hair turning into lightning. Followed by six screens of him laughing insanely and clapping wildly once he's finally defeated.
How about Matt Engarde? You get to choose which verdict he receives, Guilty or Not Guilty — but he's screwed either way, because you've just turned the assassin he hired against him. If you choose Not Guilty, Matt BEGS to go to prison. (Choosing "Guilty" eventually leads to a similar reaction.) Oh, and he claws his eyes out.
Double Subversion: When you back Luke Atmey into the corner during the burglary trial in Case Two of Trials and Tribulations, he pulls off a total nervous breakdown, complete with lapse into Talkative Loon status. He's faking it; the burglary charges are his alibi for the murder he committed that night. Once you catch Mr. Atmey as the murderer in the case's second trial, however, he repeats the breakdown word for word - and this time it's real.
Apollo Justice has another satisfying one, involving Kristoph Gavin. He taunts you about your lack of decisive evidence, but when he's told that a jury is deciding his fate, he completely loses it and starts raving about how their inferior intellects can't decide his fate. Then you get to vote on whether or not the defendant is guilty or not. You later find out he was pulled from the courtroom, laughing like a madman.
"The record will show that when the verdict was announced, special witness Kristoph Gavin... laughed. A laugh louder than any ever heard before... or since. A laugh that echoed in the halls of justice, lingering for what seemed like hours."
And the crowning moment of that particular breakdown came when Apollo mentioned that Phoenix Wright planned the whole thing. His hair goes straight up, and he writhes about, screaming Wright's name. It was completely unexpected, awesome, and probably the biggest "holy crap" moment in the entire game.
One of the most EXCESSIVE breakdowns is Dahlia Hawhorne's, and then, not in the first case where you essentially nail the final nail into her coffin OR the fourth case, chronologically the first where's she's up for potential murder, but she manages to slither away because of Walter "Terry" Fawles' suicide... IN COURT, no no no no ladies and gentletropers, case five in which she reveals herself to be channeled by Maya Fey, and Phoenix, Godot and Mia show her that for a Big Bad she's pretty pathetic, because every single last one murder she attempted to further herself in life eventually backfired in this massive Gambit Pileup, and that she never actually managed to kill anybody worthwhile personally.. the bitch FREAKS and gets sent to Hell screaming, with the Fey Magatama logo rising up in those Japanese style spirit flame things. Ah jah. ... And the case goes further still, putting the character arc of a certain prosecutor to rest..
Happens in Ace Attorney: Investigations too, probably the best example being Ambassador Alba seemingly losing entire portions of his face. Ick.
That's not the half of it. The already-old man ages about 20 years in a matter of seconds.
On the other hand, Shih-na's final breakdown is simply going to haunt your dreams for weeks to come.
The final boss of Ace Attorney Investigations 2 has a variation: instead of breaking down directly, he has a comparatively calm Motive Rant followed by a pathetic plea of "I didn't understand anything!" As this takes place at a circus, doing so sets off the nearby animals, who all line up and have a go at him.
The breakdowns in Phoenix Wright: Ace Attorney - Dual Destinies are now more over the top than ever through the new usage of camera angles. One such breakdown of Aristotle Means consists of writing a bunch of sentences that are basically alternate, lamer punishments to his really long years of prison on his chalkboard, with the audience booing at each suggestion and throwing chalk at him, and causing him to break his teeth when he tries to write another word and collapse along with his blackboard.
Even the first culprit's breakdown is rather over-the-top, in contrast with most past games: He starts trying to disarm his model bomb by biting down on the wires and yanking them around while screaming like a maniac, followed by extending his goggles to full (ridiculous) length and smashing the bomb with them. Just as the bomb stops ticking, the goggles blow up in his face, knocking him down. And just to rub it in, the bomb reactivates just as he hits the floor, announcing "GAME OVER: DISARMING ATTEMPT FAILED" to the entire courtroom.
That's nothing compared to the final boss of the game. The Big Bad turns out to be a master of disguise, and his breakdown involves removing masks of other character's heads in a Shape Shifter Identity Crisis, one after another as pieces of the courtroom ceiling fall around him, and finally just as he removes the final mask, someone snipes him from afar and he falls into the shadows of the courtroom, with his face conveniently hidden.
Clive:[[This isn't happening. It can't end this way. IT WON'T END THIS WAY!]]
The Getaway: Charlie Jolson decides to pull a Taking You with Me after his plans are foiled and activates a bomb while he and all his enemies are still on board the ship the bomb's on. He then proceeds to sing Land of Hope and Glory, making no attempts to leave.
Left 4 Dead 's AI Director is in charge of spawning the zombie hoards that players fight through. Once the rescue vehicle appears at the end of a campaign, the Director will throw everything it's got at you, quickly overwhelming any player who doesn't get on the vehicle quickly.
Dies Irae emotionally inverts this as the Big Bad Reinhard only gets closer to insane happiness as the hero, Ren, gets closer to beating him. As he is such a genius at combat, he has never felt how fun a difficult fight could be for him.
Also, listen closely to Kefka when you actually fight his final form: He laughs even longer than usual (by about 5 seconds) after saying "Life... Dreams... Hope... Where do they come from? And where do they go...? Such meaningless things... I'll destroy them all!!"
In Final Fantasy VII, Professor Hojo starts off as a calm, composed and ruthless scientist. As the game goes on however, he gradually starts to begin more and more unhinged, ultimately culminating in him going completely insane, willingly attempting to destroy Midgar to help Sephiroth, and goes so far as to inject himself with Jenova cells, fighting the party as a pseudo-Eldritch Abomination, all while gigglingmadly.
And as Dirge of Cerberus shows, death did not help his mental state. If anything, it made him worse.
Each encounter with Seifer in Final Fantasy VIII shows him edging a few steps further along a downward spiral; he starts out proclaiming himself a heroic knight pursuing a romantic dream, and ends up trying to sacrifice his former girlfriend to an insane sorceress in order to bring about The End of the World as We Know It, purely because by that point he felt like he'd gone too far to turn back. His slow breakdown is reflected visually by his long white coat, which starts off as a Badass Longcoat but is tattered and shredded by the last encounter. Unlike most villains, Seifer gets better; during the ending cutscene, Seifer's coat is back to the way it started out.
Final Fantasy IX's Kuja spends a good portion of the final part of the game hopelessly insane with rage upon discovering he's mortal and will eventually die, and was just a temporary tool of The Man Behind the Man (and that the protagonist Zidane is essentially a far more advanced model of what he was supposed to be.) Kuja ends up blowing up one world and very nearly blows up another in quick succession.
Final Fantasy XII has Vayne. After the rebel forces and his own brother Larsa beat him up, he goes One-Winged Angel and orders Larsa's bodyguard Gabranth to protect Larsa while he deals with the rebels: Gabranth decides to help the rebels defeat him instead. Beaten a second time, all Vayne has to say at this point is "BURN IN HELL, GABRANTH!" as he tries to strike him down. Vayne then limps away, bemoaning his plans and empire are crumbling around him.
Zexion of Kingdom Hearts: Chain of Memories, in both versions, though it's easier to see in the remake, what with the better animation, new and modified scenes, and quite good voice acting. The deceptive Zexion, who hates getting his hands dirty, has been spending the game flinging his comrades before him to take the fall. He slowly grows more insecure as everyone else dies, and he completely loses it as Riku sees through his tricks and defeats him in combat. Being that he was rather something of a Smug Snake, this was a very satisfying lead-in to his demise. It's SOOOOOOOOOOOOOOOOOOOOO satisfying! Yes, you may do the evil laugh here if you want to.
Also in Chain of Memories, Larxene, the sharp-tongued Alpha Bitch, who just as soon dishes out abuse as take it, really loses it when Sora defeats her once and for all. To say she is a Sore Loser is an understatement.
Larxene:No... Nooooo!! I refuse to lose to a bunch of losers! I... I'm fading?! No, this isn't... the way I... I won't...ALLOW...!
Master Xenahort in Birth By Sleep is a completely composed Chessmaster who only raises his voice in joy at how well his plans are going and in battle is very laid back and not particularly aggressive. Until he finally takes Terra's body as his own and seconds later is attacked by a newly formed Lingering Sentiment. This is the first time in the game he's truly pissed "Your body submits, your heart succumbs, so why does your mind resist!" and the resulting boss fight has him constantly pounding away at you in your face with no mercy as opposed to casually hanging back and flinging spells as before.
Though Xehanort's initial fury might not be so much an issue of Sanity Slippage as wanting to finish Terra once and for all. He was seeking to possess Terra before and probably consciously held back his more damaging attacks. Also, after being old for a while, he may have wanted to test out his new youth powers.
Hades is known to snap if things don't go his way or when somebody insults him to his face. Usually, he often calms down immediately after his snappings, but in his final showdown against Sora he doesn't; when Sora, Donald and Goofy released Auron from Hades' mind control, and so saved Hercules' life, Hades got pissed but remained in control, but when his attempts to kill Hercules by throwing Meg into the River Styx failed, and the heroes laughing at Hercules' joke afterwerd, he began to screaming: "HOW DARE YOU GET A HAPPY ENDING?! HOW DARE YOU?!" and went ballistic on them by screaming and throwing fires everywhere. When Hades goes ape-shit, you know all hell is about to break loose - and it makes for one awesome boss fight. And when he loses, he really becomes a Sore Loser:
Saix, while shown as a calm individual through most of the game, becomes utterly psychotic under the moon's influence late in the game, savagely attacking Sora and his allies during their final battle. In this case, while you have to defeat him, if the situation ever occurs in real life, the best option would be to FLEE FOR YOU LIVES!
In Command & Conquer: Tiberium Wars, Kane is cool, calm, and absolutely collected throughout the entire game, mercilessly taunting GDI and generally seeming unflappable until Killian Qatar allies with GDI. His response to this is to flip the fuck out and order the player to Nuke 'em. After Killian's subsequent execution he calms back down and resumes his usual magnificent bastardry.
Stalin in the first Red Alert game is like this as well, going from confident and snide to drunk and slightly unhinged, to breaking his subordinates' necks with his bare hands.
Anyone on Nod's side who isn't subtly assassinated gets one of these. Particular mention goes to Vega, Kilian, the Nod Warlord in Rio (real name unknown), Alexa, and CABAL (to a degree, he just went batshit crazy for no apparent reason in the last mission).
Director Boyle, the man in charge of GDI during Tiberium Wars, has one in one of the later missions. Normally he's a sly talking politician who gives off an air of both class and arrogance, but nearing the end, he meets with the commander secretly and discusses (read: rants) about how Granger is trying to take his political position.
Both the fake and real Overlord Zenon in Disgaea 2. Fake Zenon's starts with Etna thoroughly handing him his ass, and then peaks when Axel broadcasts his location onto everyone in the multiverse, sending nearly every single Overlord to his front door, ready to rip him in two. As for the real Zenon, hers begins when Adell makes it clear that he hasno intention of fighting her.
Nemo in Disgaea 4 starts off as a Magnificent Bastard, but his facade starts to crack after the Kazamatsuri family settle their differences (mostly) in a heartwarming scene. Then he absolutely loses it at the end of chapter 9, after his plan to destroy the Earth by crashing the moon into it fails, signaled by him going Laughing Mad.
In Castlevania: Portrait of Ruin, Brauner snaps when Jonathan reveals to him that his daughters aren't really his. "Snaps" is apropos, as part of the breakdown is that he presses his cane hard enough into the floor that it breaks.
Saavedro of Myst III: Exile comes pre-broken due to being trapped on two small islands in Narayan and J'nanin for upwards of twenty years. He breaks again when the player manages to deactivate the outer ice shield that's isolated him from the rest of Narayan, allowing him to see that at least one city has survived and possibly his family with them, but he can't get to them without the player's help and a third time when the player stabs him in the back and traps him between the two ice shields. "No! NO! No, no, no, no, no, no, no..."
From End of Ages: "You ... IDIOT! Moronic lump of filth! You are nothing! Puh! AHHHHHH! I needed the power! I needed it! D'ni needed ME! You threw it away to this witch and her legion of scum, the demon slaves! You have released the slaves as masters! You've turned the small to great! Curse the Maker..."
In Devil May Cry 3, through most of the game, Vergil acts as an Aloof Big Brother and Evil Twin to Dante, remaining menacing and softspoken even as he shoves a katana into Dante's gut. He then tries to open the portal to the Demon World with the Perfect Amulet and his own blood. When that fails since Lady's blood is also needed, something Arkham left out on purpose, Vergil's composure cracks.
Vergil:Why isn't this working?!
Likewise Arkham after hes defeated by Dante and Virgil and left severely wounded. He comes across his daughter, Lady, and rants about he should have the power of a demon and that what Sparda did was no different from his actions (namely sacrificing a human woman. However, Sparda did it out of reluctance since he loved his sacrifice, and she went with it willingly and it was for the good of mankind. Arkham did it purely for his own selfish ends). He begs Lady to help him and she responds much to his shock by putting a bullet in his head.
Another Capcom example in Resident Evil 5, when Wesker's overconfidence allows him to get injected with an overdose of the virus he uses to control his superhuman abilities, causing him to lose control and composure. When the heroes stop his scheme at the last minute, he exposes himself to the Ouroboros virus, mutating into a menace full of one-hit kills and screaming "CHRIS!" with vindictive rage. As Wesker had been a Magnificent Bastard for something like nine games to this point, it was quite a remarkable breakdown.
Wesker's breakdown arguably started when he found out he was just a manufactured sock puppet of Ozwell Spencer. He goes from being an enigmatic Man Behind the Man subtly aiming for power in the shadows to declaring himself to be a god and inflicting a bio-organic weapon on the entire world.
Ramon Salazar in Resident Evil 4. Though his calm and jovial demeanor is intimidating at first, eventually, after repeatedly being foiled in his attempts to kill Leon, he snaps when Leon saves himself from the pit trap in the throne room, and shrieks at one of his lackeys to "KILL!"
The Crusader games feature two different versions of this.
In No Remorse, the Silencer's continued reversals of most of The Mole's early successes results in The Mole challenging the Silencer, a bona fide Super Soldier, to single combat. (It doesn't matter that the deck is stacked, because anyone rational would have seen the character had just walked through ten levels of decks that aren't nearly as well-stacked.)
In No Regret, the Resistance strikes a major blow after the sixth mission. The LMC strike back in the next mission, but not as effectively as they'd hoped. Chairman Draygan decides to bring in an entire troop carrier of elite soldiers...and the Resistance shoots it out of the sky. He then tries to blow up the Lunar base, while he's on it. The Resistance stops the reactor overload, and he's told by the WEC'sPresident that he's not getting off the moon until he gets the situation back under control...so he pulls all troops back to the headquarters, leaving the majority of the Lunar base under Rebel control, and starts fortifying. He then tries to take the Silencer on in single combat, which worked about as well for the bad guys as it does in the first game.
Ganondorf is surprisingly calm and calculating in The Legend of Zelda: The Wind Waker; killing Link isn't even a priority for him anymore. This all changes when the King of Hyrule snatches the completed Triforce from right in front of him and uses it to sink Hyrule once again. Ganondorf's response is to let out some insane Evil Laughter, afterwards mocking the King's wish to "give Zelda and Link a new world", and proceeds to attack Link and Zelda.
Which is even more insane when you consider that without the Triforce of Power (which left him to form the Triforce), there is no doubt he is going to die. If Ganondorf had defeated Link and Zelda in the final battle, then he would have drowned with Hyrule.
Zant goes through a rather sudden breakdown when you battle him in The Legend of Zelda: Twilight Princess, changing from a very calm Evil Overlord to a spastic, shrieking mess in the blink of an eye. He went through something similar in the game's backstory, after being denied the throne to the Twili Kingdom, which may explain the sudden breakdown when you face him; it was always there and he was just holding it in (which wouldn't be that hard to do, since everything was going his way and he had no need for a breakdown...until Link and Midna storm his palace and break down his front door, that is.)
Near the end of Baldur's Gate II the protagonist finally learns what happened to Big Bad Jon Irenicus and what his plan entails. After being foiled he comes face to face with his former lover and loses control for the first and only time in the entire game.
Irenicus: I... I do not remember your love, Ellesime. I've tried. I've tried to recreate it, to spark it anew in my memory. But it is gone... a hollow, dead thing. For years, I clung to the memory of it. Then the memory of the memory. And then nothing. The Seldarine took that from me, too. I look upon you and I feel nothing. I remember nothing but you turning your back on me, along with all the others. Once my thirst for power was everything. And now I hunger only for revenge. And... I... Will... HAVE IT!
Notably, in Irenicus' subsequent appearance in Hell itself, he is once again calm, if not altogether there.
For the first time, there's also a hint of uncertainty in his threats before the fight begins, given that by this point you've already thrashed him in battle a couple of times.
Sendai in Throne of Bhaal has a rather amusing sequence where she sends villain after villain after the protagonist, growing steadily more freaked out as no matter what she does she can't seem to stop the protagonist.
NSE Director Hanson has one at the end of Second Sight: normally a self-assured and frustratingly patient villain, he begins to lose his cool when John Vattic manages to infiltrate his underground base, to the point of snarling "I'm tired of picking through this crap!" when asked to review Project Zener's files again. This is taken a step further into near-megalomania while observing the battle between Vattic and base security, as he is clearly very excited about the demonstrated uses of psychic powers. However, the final stage of his breakdown is when he realised that Vattic and the other psychics have managed to kill every last soldier at his disposal, and when he discovers that while the window he's hiding behind is bullet and psi-proof, the frame supporting it isn't. In a matter of seconds, he goes from a smirking, self-satisfied manipulator to a frightened and helpless tourist surrounded by mutated psychic children who want to eat him alive. His last words say it all:
No... no, stay back... what do you want?! Stay away from me! I said STAY AWAY! Don't touch me— AH, YOU BIT ME, YOU LITTLE BASTARD, YOU AAAAAAARGH NOOOOO AAAAAAAAAAAAAAAAAAAAAAARRRRRGHHHH!!!
Done by Caulder/Stolos of Advance Wars: Days of Ruin/Dark Conflict, pleading for help as he dies in the destruction of the Owl's Nest. The NA Version makes the breakdown even more apparent:
Caulder: N-no... NO! What have you done?! I'm...I'm dying... I'm DYING! I have killed so many clones, but I am different! I am unique! I am ALIVE! Help me! Please! Someone! Help me! I don't want...to die...
In the ending of Sonic and the Secret Rings, Erazor Djinn taunts Sonic about his immortality and how he can come back again and again... Until Sonic pulls out his lamp, reversing Erazor's grin. After Erazor is forced to bring back Shahra and reverse the damage he's done via two wishes, Sonic makes the third wish, to seal him in his lamp forever. This is where Erazor REALLY breaks down:
Erazor: Shahra, I know you're there! Please, stop him! We can start over, the two of us! I swear it! I swear it...! THE WORLD IS MINE! I CANNOT BE DENIED BY THAT FILTHY RAT! WHHHHHHYYYYY?!?
Sonic's wonderfully calm response was to correct Erazor that he was in fact a hedgehog, not a rat.
In the Anarch or Lone Wolf endings, after being slashed half to death by the PC and left for dead in his penthouse suite, he finally opens the Ankaran Sarcophagus with the key that the PC was kind enough to leave him. However, when the lid sides back, he discovers that the Sarcophagus has been filled with explosives, all set to detonate in ten seconds; Lacroix has just enough time to let out a long drawn-out burst of maniacal laughter before he vanishes in a fireball.
And in the Camarilla ending, the PC refuses to give him the key; after Lacroix's attempts at dominating you fail, he falls to his knees, begging and sobbing for you to give him the key, raving about the imminent destruction of all vampires in Los Angeles. He eventually falls silent when your new Camarilla allies arrive to arrest him.
And finally, if you side with the Kuei-Jin, he completely snaps, ranting and raving at the PC long enough to keep him from opening the Ankaran Sarcophagus before your new "allies" arrive and give both exactly what they deserve.
Andrei the Tzimisce suffers his own breakdown when the PC meets him for the second time, ranting and raving about Gehenna and accusing the PC of being a puppet, before transforming into a monstrous war-form and attacking in a frenzy.
"I will do it myself, if I must... and you, you will be purified. It is the blood he is speaking through, the blood of all the pawns... IT ALL MUST BE PURIFIED!"
Oh man, Sakaki of .hack//G.U. goes through this TWICE. Doesn't help that he's really a kid pumped full of something he really shouldn't be, but he had it coming.
Rugal Bernstein of The King of Fighters fame has a healthy helping of TWO of these, in 94 and 95. In 94, beat him and in a rage, he blows up his own aircraft carrier with himself on it. In 95, beat him and as the Orochi power consumes him, he screams in indigation at his fate (compounded by Iori telling him he wasn't of the bloodline so he couldn't control it).
"Even with my new power I lost. What? My body.....????? NO! To meet such a fate! But I'll be back... YOU JERKS!
Goenitz in 96 subverts this in almost all of the endings, even when he's beaten, he retains a Smug Snake demeanour. Its played straight in the Kyo/Iori/Chizuru ending, however, when Kyo and Iori deliver the coup de grace on him, he screams out, wondering why there's no wind blowing.
Then there's Clone Zero in 2000. Once beaten, he tries to kill everyone in his hideout with the Zero Cannon....,which isn't working. He's constantly asking why it won't work, all while hammering the activation button repeatedly.
And finally, Saiki in XIII. Once he's beaten whilst in control of Ash Crimson's body, he tells Ash they can start over and tells him to go through the gate of time...only for Ash to do absolutely nothing whilst Saiki is telling him to go through, degenerating into screaming at him and when the gate finally closes, Saiki's begging for his existence, crying that he doesn't want to die before he vanishes, a victim of a Time Paradox.
In the backstory of Diablo, King Leoric is possessed by Diablo and effectively starts having a Villainous Breakdown while he's still a good guy. He doesn't remain good for long when that happens. He starts getting increasingly paranoid and less sane, until finally when Diablo leaves him, unable to take over completely, he's a raving madman who has to be killed by his own most loyal knights.
Diablo himself has one in Diablo III; around the middle of the boss fight with him, he loses patience and uses one of his ultimate attacks on your character: traping you a Realm of Nightmare where, according to him, no one ever managed to escape from. When you stillmanage to get out of it, he completely loses it:
Diablo: "NOOOOO! This wretched light must be eradicated!"
Sakura in Fate/stay night. Going from zero self esteem up to being able to say A God Am I justifiably did give a major confidence boost. Yet, when Tohsaka without having the power of the Grail to draw on still effortlessly matches her, she freaks even more than she was before. In a manner of minutes while Tohsaka casually blasts all the shadow giants she makes one by one, she's reduced to an incoherent screaming wreck about how it was pure chance that made it her that lived among the Matou and not Tohsaka. Her will to fight is seconds from vanishing utterly when Tohsaka eggs her back into fighting spirit. She gets better.
Gilgamesh in Unlimited Blade Works experiences one when he realizes Shirou is beating him with his replica blades. He quickly goes from condescending god-king to shouting "Bastard!" over and over again.
At the end of Need for Speed: Most Wanted, Cross, the cop who's been after you for the whole game, gets one (even though he's not really villainous). Bonus points for being a Shout-Out to The Professional:
Cross: You had the most wanted street racer in Rockport in your hands... and he got. Away? (turns to his partner) I want everyone after this guy.
In fact, he then calls you in the middle of the ensuing chaos (you're being chased by every police unit in the city with no chance of proper escape) to rant about how he's going to take you down, and it's surprisingly not at all calm. In the sequel, Carbon, he ends up quiting the police department to become a bounty hunter, just so he can take you down.
In Batman: Arkham Asylum, the Riddler goes from insulting you to accusing you of cheating to threatening to blow up Gotham as you solve more and more of his riddles. Also, the Scarecrow panics as Batman manages to shake off the effects of enough fear toxins to drive 10 men insane. The climax also stems from Joker throwing a tantrum and accusing Batman of 'spoiling my fun!' when Batman refuses to succumb to the Titan strain that Joker has infected him with and become a monster.
As if the Soulstorm expansion to Dawn of War weren't horrible already, as the Chaos stronghold mission progresses, Carron, supposedly a powerful Chaos Lord of the Alpha Legion, actually breaks down crying as his shrines are destroyed and the enemy advances, culminating in him snivelling and whining some nonsense about flowers and fleeing the battle. Contrast with Eliphas, who remains serene and mocking throughout, Crull, who remains psychotically insane throughout, and Bale, who merely gets angry when Sindri betrays him.
Although there isn't much room for it in the Metroid series (outside of possibly Prime's Pirate logs), the 1994 Super Metroid comic features one of these later on, when Ridley is informed of Samus's progress. He actually leaves the planet and abandons his command, telling his informant that they should all just listen to Mother Brain instead.
Cyrus in Pokémon Platinum might apply, especially in the Distortion World. He spends half the game saying he's disregared all emotion, seeing them as weakness and useless. One can't blame him for losing it, being dragged into that world by Giratina.
There's this, which he says before he utterly demolishes your team in the Distorion World:
Cyrus: "Why should I run and hide from the world and have to wait quietly? My aim is to rid our world of the vague and incomplete thing we call spirit. By freeing ourselves of that, our world can be made complete. That is my justice! No one can interfere! I won't lose! Not to that shadowy Pokemon! Not in any worthless world!
And when you do managed to defeat him, he has this to say.
Cyrus: "... Don't think that you can defeat or capture that Pokemon. This bizarre world is none other than that Pokemon itself! Capturing it or defeating it will make this world disappear! Very well! Do what you will! Rather than repairing the world, you're going to destroy it for me! Do it. You inherit my legacy."
Plus this, once the player defeats/captures Giratina.
Cyrus: "That Pokemon... That shadowy Pokemon was captured/defeated?! Your doing so means that this irrational world will remain in existence! Does that make it impossible for me to create a new world? Even if I made new Red Chains, the new world can't be made! Why?! What compels you to protect the two worlds? Is spirit, a vague and incomplete thing, so important to you?! Silence! Enough of your blathering! That's how you justify spirit as something worthwhile?! That is merely humans hoping, deluding themselves that they are happy and safe! The emotions broiling inside me... Rage, hatred, frustration... These ugly emotions arise because of my own incomplete spirit!"
What makes his growing insanity even more apparent here is the fact he says 'Silence! Enough of your blathering'. Even if the hero wasn't always silent, he/she didn't say a thing.
Cyrus: "...Enough. We will never see eye to eye. This, I promise you. I will break the secrets of the world. With that knowledge, I will create my own complete and perfect world. One day, you will awaken to a world of my creation. A world without spirit."
In Pokémon Black and White, Ghetsis undergoes one of these after the player has caught the legend and defeated N - Ghetsis's very manipulative plan all hinged on N beating the player, and making everyone give up their Pokemon as N was raised by him to believe that they should be separate. The truth is, Ghetsis just manipulated him all his life, just so he could be the only person to have Pokemon and be able to rule Unova. He calls N an inhuman monster, which is called out by Alder and Cheren, who noted his hypocrisy. He gets even worse after you beat him.
Ghetsis: "I AM PERFECTION!!!"
It got worse as of Pokémon Black 2 and White 2. When he's first encountered on the Plasma Frigate, Ghetsis appears to have become something of a mad hermit, sitting in a secluded security office giving signs of Owellian surveillance linked around the ship. Cranked up to eleven toward the climax of the game, where he attempts to use Kyurem to freeze the protagonist alive. By the end of the game, multiple defeats at the hands of the protagonists and the destruction of his life's work have utterly broken Ghetsis, reducing him to an inaudible, non-functioning vegetable. Wow.
Comrade Black from De Blob. He really starts to freak out near the game's end.
Overlord GAIA from Digimon World 2. He was able to (though not perfectly) form coherent sentences when he is first encountered. However, he seems to break down after Akira defeats his first form.
Overlord GAIA: "I... am the most powerful... the most powerful... the most powerful... the most powerful... the most powerful..."
Akira: "Is it still capable of fighting?"
Overlord GAIA: "I... am ultimate... I... ultimate... I... ultimate..."
Sly 2: Band Of Thieves has a very nice example in the form of constable Neyla. All through the game she plays everybody off of everybody else in order to get what she wants. The more you foil her plans and gather the Clockwerk parts for yourself the more short tempered and less composed she becomes until the grand finale she's screaming with rage, swearing to hunt you down and kill you in your sleep.
After spending two entire games as a masterful, unflappable manipulator, Nyarlathotep from Persona 2: Eternal Punishment starts to lose it after the party penetrates the numerous illusions and mind games he scatters throughout his lair. He's reduced to incoherent screaming by the end of his boss fight, still convinced he's unbeatable.
"I WON'T ACCEPT IT! INVINCIBLE! INVINCIBLE!"
Adachi in Persona 4, despite being both a Smug Snake, keeps his cool right up until the protagonists find him. Even then, he manages to remain composed enough to berate and mock them. However, when he is repeatedly called out for being nothing more than a criminal, he finally breaks down and starts cursing and yelling at the protagonists, telling them "[They] have no idea of what kind of shit I've had to go through!" And then he summons his persona and the boss fight begins.
Teryn Loghain in Dragon Age: Origins slowly loses it throughout the game, but really flips out if you turn the Landsmeet against him. He calms down again after you kick his ass and is even willing to accept execution since he now believes that the Grey Warden really can defeat the Blight.
Howe: It seems you have made something of yourself after all. Your father would be proud. I, on the other hand, want you dead...more than ever now.
Knight-Commander Meredith in Dragon Age II has a moment of doubt near the end of the final battle in which she questions whether she is doing the right thing, but quickly shakes it off.
During the second chapter, Mother Petrice (the Chantry priest who believes the ends justify the means to get rid of the qunari) tries to set you up for killing the viscount's son. When you kill the fanatics she sics on you, she brings in the Revered Mother and tries to spin it to make you a monster. The Revered Mother will have none of her shit, quietly calls her out, and tells Hawke to fetch a guard. The look on her face as she realizes that the Chantry as a whole does not support any actions necessary to oust the qunari is wonderful. Then a qunari kills her. And everything goes to hell.
In the Templar path, Orsino snaps, sacrifices his fellow mages to use their corpses for Blood Magic and indulges in a bout of maniacal laughter right before he uses the bodies to turn himself into a Harvester golem. In the Mage path it's more of a Despair Event Horizon.
However, Orsino's moment of mania can be ruined if Bethany is in the Circle and Hawke convinces her that Orsino supported the man who killed their mother.
The fact that two of the seven people in the group that defeated him are his surrogate mother and his overprotective little brother, the exact people whose attempts to protect him gave him that complex in the first place, also didn't help.
Speaking of the spoiler, Helio has a breakdown himself. While not as rabid as some other examples, he breaks his cool demeanour long enough to scream his head off at Ethan and inject himself with Psycho Serum during the aforementioned (Villainous?)Heroic Sacrifice.
The two villains from the Modern Warfare series have both done this. In the first game, Imran Zhakaev tried to start a global war, starting in the Middle East. After his son commits suicide after you have him cornered, he tries to NUKE THE EAST COAST as payback. In MW 2, Shepherd's plan goes perfectly until Soap and Price escape the trap he laid for them at the boneyard. Cooperating with Makarov, the two find Shepherd's hideout and go on a rampage through it, thwarting every attempt made to stop them, Shepherd finally resorting to BLOWING UP THE BASE with his soldiers still inside in order to kill them.
It gets better: up to that point in the game, he'd occasionally mutter 'Kuwabara, kuwabara' to himself (being a superstitious chant to ward off lightning storms). Cut forward, and he laughs in the face of a brewing storm. Guess how he met his end?
Sovereign also briefly lost it earlier in the game, but it's very subtle. When Saren learns that Shepard has used the Prothean Beacon, the interior of the room turns red and Saren has a very out of character tantrum. Since he's being indoctrinated, one can infer this was due to Sovereign briefly taking control and venting his frustration through him. In fact, you can even hear Sovereign's voice faintly underneath his.
A minor villain near the start of Mass Effect 2 gets increasingly frustrated at her troops as Shepard gets closer to her ("There are three of them. THREE! Anything can be killed if you'd just do your damn jobs!").
At the end of Mass Effect 2, you have the option of majorly screwing the Illusive Man over. In the conversation with him afterwards he reveals his true colours and abandons any notions of being Affably Evil.
Illusive Man: Strength for Cerberus is strength for every human. Cerberus is humanity! I should've known you'd choke on the hard decisions, too idealistic from the start!
Illusive Man: Don't turn your back on me, Shepard! I made you! I brought you back from the dead!
Archangel's, AKA Garrus, recruitment mission has you decimating the three united mercenary gangs that have united to take him down. All the gang leaders have their own little variant, but Tarak gets in the best one: he pilots the gunship Archangel had shot down before the mission started, screams that he "thinks he can screw with the Blue Suns", and plants a missile in his face.
In the Paragon ending for the Overlord DLC, Doctor Archer desperately and frantically tries to justify putting his brother through the titular horrific experiment. When Shepard angrily rebukes it and states that he/she intends to take David away so he can get treatment, Archer finally snaps and pulls a gun. Needless to say, it doesn't work.
The real kicker is Dr. Archer has been arguing that David should remain with him so Archer can look after him. What does he shout when Shepard tells him he's taking him away to be treated? "No! Stop! He's too valuable!"
In Lair of the Shadow Broker, the Shadow Broker has an excellent breakdown when Liara taunts him with information about his past despite him being unknown to everyone else in the galaxy. He picks up his desk and throws it at Liara, Shepard, and whoever else is there with them.
In "Arrival," Harbinger, who is generally unflappable even when you're about to blow the Collector Base, actually becomes aggravated.
"Shepard....you have become an...annoyance."
Speaking of Arrival, the indoctrinated Amanda Kenson starts panicking after Shepard wakes up, and only gets worse as Shep tears through the Project guards, eventually becoming a shrieking tantrum-throwing mess once Shep confronts her at the reactor core.
In the endgame of Mass Effect 3, the Illusive Man has one after Shepard and Anderson make him realize that he's indoctrinated. He goes from calmly trying to persuade Shepard of the virtues of controlling the Reapers to...
"NO! I'm in control! No one's telling me what to do!"
Indoctrination, according to the Codex, causes higher mental functioning to decay, eventually leaving the victim a "gibbering animal". Apparently, while on the way, it has humans pass through a "whining child" stage.
While most commonly interpretated as an example of The Bad Guy Wins, the Glamour Failure when Shepard choose the Refuse ending could be considered this; the Catalyst is freaking out as it realises that its destruction is assured, even if this cycle's inhabitants will be the Doomed Moral Victors of a Pyrrhic Victory, and it will die on the terms of those who shun it and all it stands for, rather than ending the cycle on its own terms.
During a mission in ME3, if you killed the Rachni Queen back in ME1, then you get to meet a Reaper-created clone of her. She requests that you release her, so that she can give you assistance to defeating them. It's recommended that you don't, as she'll kill most of the Engineering Corps, and remove herself from your War Assets. If you take the smart desicion, and leave her to die, she FLIPS OUT, screaming through dozens of dead krogan at her offspring to kill you.
How many characters from The Witcher? The Reverend, The Professor, and the hammiest of all, Jacques de Aldersberg.
Kael'thas Sunstrider, who managed to hold onto his compousure through one defeat and disfigurement, finally snaps when you defeat him for the last time in the Magister's Terrace:
Kael: "My demise accomplishes nothing! The master will have you! You will drown in your own blood! The world shall BURN!" *screams*
Ragnaros, the Elemental Lord of the Firelands, is quite confident that he'll be burning down all of Azeroth until a dozen or so plucky adventurers come in and start kicking him around.
Ragnaros: "No, nooooo... this was to be my hour of triumph..."
Deathwing the Destroyer has one of these at the end of Cataclysm, in that after having his protective armour torn off and shot through the chest with the Dragon Soul, followed by falling into the Maelstrom, he begins to break down and fall apart, sprouting molten tentacles from all over his dissolving body. Alongside this, he loses the last vestiges of sanity completely, devolving into a screaming, raving monstrosity attempting to destroy anything near him.
Deathwing: You have done NOTHING! I will tear your world APART!
After defeating all four tentacles...
Deathwing: I AM DEATHWING! THE DESTROYER! THE END OF ALL THINGS! INEVITABLE! INDOMINABLE! I! AM! THE CATACLYSM!
Kel'Thuzad: No!!! A curse upon you interlopers! The armies of the Lich King will hunt you down! You will not escape your fate...
In the Frozen Throne expansion for Warcraft III, Anub'arak has a little one when he and Arthas get confronted by the Forgotten One. He gets better, and then he and Arthas kill it:
Anub'Arak: This Cannot Be!...Look to your defences Death Knight! Fight as you have never fought before!
Arthas has a reverse breakdown at the end of Wrath of the Lich King when Frostmourne is shattered and his own soul is released along with all of the others the blade stole. He regains his sanity right before dying in the arms of his father's ghost.
In the Siege of Orgrimmar, Garrosh becomes a Willing Channeler for Y'Shaarj, and begins raving screaming about "MY WORLD" before dying with a rather tear-jerking This Cannot Be!.
Heavy Rain employs this trope if Ethan doesn't show up at the warehouse of the final chapter, but Madison and Norman do, either together or separately. The Origami Killer flipssince such a scenario goes against all of his plans.
General Adams from Killzone has one when one of his lieutenants informs him that the player's squad has destroyed an important bridge, leveled a supply base and killed an entire platoon. He then introduces the lieutenants head to his desk. Repeatedly. And not very subtle.
In Fallout 3, Should you not have John Henry Eden self destruct, taking the whole base with him, then, during the very last quest, if you tune in on the Enclave radio station, the "stress" (If A.I.'s can get stressed that is.) of the Brotherhood of Steel having just launched an assault to retake Project Purty from the Enclave with the Brotherhood's most elite squad, as well as a giant practically indestructible robot, has caused the normally calm, almost Affably Evil "President of the Enclave, President of the United States, President of your hearts" into an even more sinister voice. Just read the transcript.
Eden: We stand now, at the precipice. A great nation once more threatens to crumble, to topple into the sea of lawlessness and despair that have ruled us all for over two hundred years. In short, my dearest America, we. Are. At. War. Even as I speak these words, fearless Enclave soldiers are fortifying their positions at the great water purifier. Bracing for an inevitable assault. The Brotherhood of Steel, in their arrogance, has claimed Project Purity as their own. They would steal the Enclave’s work. Steal America’s water. It’s only a matter of time before the traitors march on the purifier, and attempt to take it by force. Let them come. Wave upon traitorous wave will crash upon the Enclave’s walls. The Brotherhood of Steel will fail. All those who oppose the Enclave will fail. I am President John Henry Eden, and this is my pledge: No one, NO ONE WILL TAKE THIS GREAT NATION AWAY FROM ME! *Eerily calm* God Bless the Enclave. God Bless America. And it just repeats over and over again.
In Fallout: New Vegas, Benny is completely smooth and calm throughout most of the story, until you kill his four bodyguards at The Tops, resulting in a priceless Oh Crap and his fleeing in desperation. He gets another if you have him crucified by the Legion.
Similarly, if you completely deny Mr. House the Platinum Chip, he flies into a rage about how far he's come and he's not letting some random courier screw up his plans. He'll then tell you that you don't have to fear him, just the Securitrons in the room. Also, if you bust into the control room and confront the real Mr. House, all he can do is rage helplessly and ask you why you would destroy Vegas' last hope.
Father Elijah from the Dead Money questline also has a very impressive Villainous Breakdown if you seal him in the vault forever.
Sequences 8 and 9 of Assassin's Creed: Brotherhood are essentially one long breakdown/Humiliation Conga for Cesare Borgia. He loses all his supporters, kills his father, the Pope, and is betrayed by his sister, causing him to lose the Apple of Eden to Ezio Auditore, the mastermind behind his family's decline. Then the remnants of his army are destroyed with the Apple-wielding Ezio and his fellow Assassins, while the Cardinals - whose appointments Cesare had paid for - turn their backs on him, backing a family rival to succeed his father as Pope. He's finally driven out of Rome by Ezio's supporters and arrested by a general whose family he'd pressed into service, then dragged away by his former elites — they're the PapalGuards after all. He escaped a year later and made an attempt at a comeback in Spain, under the command of a relative in France, but Ezio followed him — thanks to the Apple — and fights through his entire army alone, then manages to finally defeat Cesare in personal combat. At this point, all he can do is rant and rave about how no man can kill him, so Ezio leaves him in the hands of Fate...by dropping him off the castle wall.
Even his would-be Badass Boast of "If I want to live, I live. If I want to take, I take! If I want you to die... you DIIIIIIE!" counts, since it's declared when Lucrezia reveals that their father had poisoned him, this being after his father talked down to him for starting the whole mess and denied him access to the Apple of Eden or funding to continue his military campaign in Romagna. Depending on how much side content the player has done before this point, you get to see more of just how badly things had fallen apart for the Borgia regime, yet Cesare is just finding this out now.
Rodrigo Borgia also has this after Ezio defeated him in a fist fight and the Vault had not opened for him. Rodrigo simply screams "THIS IS MY DESTINY!!! ME! I AM THE PROPHET!!!!" only to request that Ezio kill him when his so-called destiny is denied, but Ezio chooses instead to leave him alive with the knowledge that he was defeated and that his decade-long plot was for naught.
The first game had Sibrand, a Templar who'd become homicidally paranoid as his fellow Templars were felled by an Assassin's hand, particularly since he'd learned from the Apple/Piece of Eden that there was no afterlife.
This game also had Warren Vidic, starting out as a smug snake only to later rant angrily when Assassins attempt a break-in of the Abstergo facility and accusing the player character Desmond of having orchestrated it, despite Desmond having been estranged from the Assassins for a decade.
Assassin's Creed III has quite a few villainous breakdowns. One from Vidic as Desmond makes short work of the Mooks sent to stop him, and killing Cross. Charles Lee also has one after Connor kills Haytham, swearing to destroy everything Connor holds dear: his tribe and the Homestead, and he's gonna make him watch.
In RosenkreuzStiletteIris gets a Villainous Breakdown in the form of laughing madly as she finally figures out where Spiritia got all the energy she destroyed her Iris Machine with. While Lilli wonders what's wrong with her, this is also where Tia hits her with a You're Insane!: "Iris, have you lost your mind!?"
Iris: Ah... I get it now! So that's what's going on! AHAHAHAHAHAHA!
In Rosenkreuzstilette Grollschert, the game's alternate mode, she also gets one when Grolla gets to confront her in battle again in the final stage. Iris gets an Oh Crap look on her face and says "...Impossible. There's no way a simple commoner can set foot here..." Grolla asks her how special she thinks herself to be and that's where she finally reveals that she's a reincarnation of Rosenkreuz, blessed with absolute power and unparalelled brains, claiming to be a child of God himself. Grolla doesn't care if she's a god, a human, or even an insect - her blade is telling her to spill her blood anyway, and she's compelled to comply. She infers that she's always willing to rip her apart just the same. Irisdoesn't take that too well. "You pompous maggot...! I shall show you the limits of a commoner!"
In Valkyrie Profile 2 Silmeria, Lezard completely loses all composure at the very end of the game, after Alicia absorbs the three valkyrie spirits and becomes the Valkyrie herself, taking Lenneth's spirit beyond his reach. Despite the insanity displayed by this character throughout the series, that is the only time we ever see such a complete loss of control.
("The Lenneth Valkyrie I sought is no more and it was you who killed her, IT WAS YOOUUUUU!!")
("Lenneth's spirit, ugh Lenneth's soul, IT ALL BELONGS TO MEEEE, NOW DIE, YOU DAMNED HUMAN!!")
Malefor from The Legend of Spyro has a rather subtle one at the end of Dawn Of The Dragon. His final confrontation with the heroes has him being Faux Affably Evil and toying with him, taking great joy out of manipulating their emotions with his Hannibal Lecture. But then, Cynder manages to break free of his control thanks to The Power of Love she has for Spyro. The result is Malefor getting enraged for the first and only time in the entire series. Throughout the rest he's been a calm, cunning, and extremely effective Chess Master who is always in control. The first time it changes is the first time he loses his cool and gets angry.
Drakath: I will not be denied my kingdom again. Sepulchure: *Cough* You think this will stop me, fool?! I will not be killed by the likes of you, worm... Drakath: Perhaps it won't stop you, but it gives me a head start. (starts absorbing energy from the Ultimate Orb) It— It's magnificent! Sepulchure: Your living body cannot handle the power! I will watch you burn and then spit on your ashes! Drakath: Fluffy! To me! Sepulchure: NO! AARRGGHHHH! The castle explodes.
Vath, the 3rd lord of Chaos in AdventureQuest Worlds, is a Smug Snake who enslaved the dwarves to have them forge enough Chaos Gemeralds to hatch the Rock Roc. Then when the hero points out that the dwarves were already freed by him/her and are winning the war against his drow soldiers, Vath loses his cool. Cue Red Eyes, Take Warning.
And after the battle, he's pissed at the hero for a reason why the dwarves chose him/her as their champion. Thinking he/she's overconfident, he stands back up, calls his Chaos Dragon Amulet, and angrily attempts to command Stalagbite, his dragon that he enslaved, to get to his feet and destroy him/her. The hero uses this as his/her chance to use Accidental Aiming Skills to throw the Legendary Sword of Dragon Control at his Chaos Dragon Amulet, destroying them to Vath's sudden despair. Stalagbite regains control of himself and proceeds to attack Vath. Cue Oh Crap from Vath himself.
Kitsune, the 4th lord of Chaos, counts as well. He's a Magnificent Bastard who's a Shout-Out to the Shredder, cares deeply for hisYokai brothers and sisters, is rarely cruel, and uses his Chaos powers to place Daisho under a spell and claim Yokai Island for the Yokai and restore it to its former secluded sanctuary. Then, the hero uses the Hanzamune Dragon Koi Blade to seal the rift pouring a waterfall of Yokai flooding the island out back up, which is something Kitsune didn't expect. He sees the hero as more of a problem than he first thought and decides to re-open the rift after dealing with the hero himself.
Kitsune: I can see that hero is more of a problem than I first thought. I cannot allow anything to interfere with my plans. The rift must be re-opened... but first I have to deal with this LEGENDARY DRAGON myself.
After the battle, the hero points out that the residents of the island still respect and honor the Yokai while Kitsune himself got greedy. Kitsune boasts that his Yokai brothers and sisters have always been superior to humans and starts running around invisible. The hero, while rapidly swinging the sword around, at one time accidentally tears open a rift in front of Kitsune to his horror, and he screams "No!Not like this! It can't end like this! I won't go back to the Yokai world!", lets loose a Big "NO!", and gets sucked into the rift after which the hero closes it back up.
Ledgermayne, the seventh lord of Chaos, isn't too happy that the hero is interfering with its plans to sap all magic from Lore by destroying the Mana Golem. It attempts one last time to convince the hero to return to his/her home and trouble it no more and not attempt to fight it with the Supreme Arcane Staff with the shards of the Chaos Focus Gem that it shattered earlier accepted into it. The hero points out that Ledgermayne left a few shards of the gem behind and shows it the staff itself. Ledgermayne sees it as fascinating and realizes that the hero can't be dissuaded from the self-destructive course as it called it. It decides that the hero must be dealt with as the hero challenges it to a fight. After the fight, the hero prepares to use the staff to finish off Ledgermayne. When the staff doesn't work, Ledgermayne decides it's wasted its time on him/her and attempts to kill him/her with one last attack, but Drakath appears and focuses his Chaos powers into the staff, replacing the shattered gem allowing it to blast Ledgermayne. Ledgermayne lets out a Big "NO!" and becomes converted back into the raw mana from which it was made.
26,000 years prior to the End of All Things event, a portion of the Frostval events, Kezeroth the World Ender sought to bring about the end of the world by freeing the ancient beast Quetzal from its icy prison that floated among the stars. His plan to do so was foiled by Elim, and when that happened, the hulking juggernaut normally full of Dissonant Serenity lost his composure big time, taking his anger out on Elim because his whole life that he had waited for the night that Quetzal's comet was to be brought down to Lore had been wasted and using his massive warhammers that he wields with ease to beat him to death in a murderous fit of rage. In the present, he loses his composure again after finding that Quetzal, whom he had been given a second chance to free and unleash upon Lore, had been beaten down by "a handful of pitiful heroes" as he calls them, afterwards using the Sword of Hope that they were going to use to finish their job of finishing off and destroying Quetzal for them. This act really shot him in the shoes because, had he not done so, Quetzal would have regained its strength anyway.
Though the "villain" status is questionable, Popola from NieRgoes from a calm Chessmaster to shrieking, batshit crazy when her sister dies.
The final boss of Trilby The Art of Theft. First he smugly taunts you about how he's going to torture you and how you'll beg to give xj unit to getting slightly scared after you hit the first wire to desperatly begging for you to stop and surrender to angrily yelling about how Trilby killed them all Trilby escapes
Tobin from In the 1st Degree. If you, the prosecutor, did a very good job playing the game, then Tobin will called to the stand. You are trying to drive Tobin into this. There is some trial and error involved, but if you do it right, you get to watch Tobin completely lose it in front of everybody right there in the courtroom. When that happens, you know you have won.
in the Gears of War trilogy, Myrrah suffers this in the third installment. In the first two games she is a detatched, enigmatic figure. Always cool and collected even when Marcus storms her throne room. However in the third game she has lost her composure after being pushed to the brink of extinction, sneering and taunting Marcus at every opportunity.
In Thief: Deadly Shadows, the Hag breaks down weeping and begging the Keepers surrounding her to stay away after Garrett activates the Final Glyph and destroys all Glyph magic, reducing her to a powerless old woman.
Gamall: Back...back with you!...Old...so old...(breaks down weeping)
In Star Fox 64, the alternative way to beating Mechbeth in Macbeth has the pilot desperately trying to stop the train. He loses it when he's about to slam right into the supply depot, causing the depot to explode along with the train, obviously killing him.
This is less a mental breakdown and more genuine and legitimate panic, since the brakes failed on him and he anticipated what was about to happen.
In Sid Meier’s Alpha Centauri, when fighting a war with an enemy faction and pushing an enemy back and taking over their territory, the opposing faction leader will begin sending you messages. They start off with the usual rounds of offers for peace, maybe trying to extort a technology or money out of you for a ceasefire. Then they'll offer a general ceasefire. Then, if badly losing, they may offer an unconditional surrender. Or, if they're more erratic, you get to witness a gradual Sanity Slippage as the faction leader keeps sending you messages telling you that they will completely wipe out your faction, that Planet isn't big enough for both of you, and that s/he'll crush your [insert derogatory description here] followers under his/her might, and will keep on spouting that over and over until you finish them off.
As much of a Magnificent Bastard as he may be, Yuuki Terumi from BlazBlue tends to get rather loud when his schemes show signs of going off the rails. Murder usually follows in these cases.
In Carl's bad ending in CS, when he realizes that Carl is a vital piece to Takamagahara's puzzle, he orders Mu to stop her attacks, swears at the top of his lungs, immobilizes Carl, butchers Ada/Nirvana, and demoralizes Carl further before killing him. He's back to his normal composure when he's done with the butchering, however.
In Valkenhayn's bad ending, Terumi is having a ball slaughtering the Silver Wolf, going so far as to give him orders as if a dog ("Speak! Roll over! Play dead! PLAY DEAD, GODDAMNIT!" *laugh*), before Phantom teleports him away. Before he could turn his blade on her (or it?), he realizes Takamagahara still has him on a leash, and could reset on him if he killed Valkenhayn early, so he calms down quick.
In the ending to Makoto's story, while he doesn't crack up as much as the others, his voice and facial expressions once Tsubaki is away show that he is barely restraining Ghirahim-esque contempt for Makoto for unknowingly dividing his plans by zero. He bursts into screaming when Rachel steals his quarry right out from under him soon after. And unlike the prior, the damage is permanent - when he sees Makoto chatting with Jin in his story, Terumi decides to introduce himself with a knife to Makoto's back (Jin parries the blow), and in Makoto's arcade mode, he is seen periodically bursting into laughter and eating Adventus.
In BlazBlue: Chronophantasma, Terumi gets in a fight with Hakumen, who begins setting up the Susano'o Unit's Time Killer function. While Terumi taunts at how easy he can avoid it, Trinity Glassfield tethers him in place, leaving him prone to Hakumen's assault with no chance of survival. In the time he has left, all that remains is hatred towards Trinity, who he kills and tosses off a cliff before the last grain in his hourglass falls - all as one last, twisted act of revenge.
Also, Relius joins the fun. He's just about ready to seize the Lynchpin and fulfill the magnum opus he built up for years, and while he doesn't have Rettenjou at his command (Bang's carrying it), he has Bang's love interest (Litchi) and young apprentice (Carl) as pawns to coerce it out of his hands. What Could Possibly Go Wrong? Tsubaki Yayoi (fresh off her brainwashing) and Makoto Nanaya (a separate target of Relius', who helped Tsubaki break free) run decoy duty for Litchi and Carl, and Valkenhayn intercepts Relius in turn, leaving Bang free to activate the Lynchpin on his own terms, flushing all of Relius' work down the tubes. The double whammy of his desire for perfection being undone in front of him and Imperator Librarius leaving him to his doom, Relius completely shuts down, losing his will to go on and leaving himself to Valkenhayn's mercy before Carl and Litchi intervene - the terms being that Relius will help Carl restore Ada before commencing his atonement for his laundry list of atrocities. All Relius had to say on that is that he looks forward to the last part.
In Baten Kaitos Origins, both Nasca and Heughes have major breakdowns if you destroy their machina armas. If you opt to spare them, they go crazier, with Heughes screaming threats and Nasca brokenly pleading for a fight.
Baelheit is mostly calm throughout the story, but he goes absolutely ballistic when you confront him at the climax, to the point where he shoots his daughter in the face, just to make a point. And then after Verus reveals himself, he changes from the cool authority figure you've known to a demented, cackling fiend.
In the MOTHER series, this happened to Giygas between games. At the end of MOTHER 1, Ninten and his friends sung to him the lullaby Maria used to sing to him. After being defeated this way, he vows to return. By the time of EarthBound, he became so powerful that not only did he break down mentally, but physically as well, and he now needs the Devil's Machine to keep his form.
In Call of Duty: Black Ops 2, the best ending has Raul Menendez imprisoned for life after the complete and utter dissolution of his grand scheme, up to and including his secret escape gambit— this results in him being forced to watch from his cell as Chloe goes on the Jimmy Kimmel Show and publicly mocks him, causing him to completely flip out and bash his face against the TV monitor until his forehead bleeds.
In The Elder Scrolls V: Skyrim, Alduin helplessly shrieks in protest as his body slowly crumbles after you strike the final blow since he can't accept the reality of his impending death. His voice even seems to go an octave or two higher as he screams "No! I cannot die!" in the dragon tongue.
Star Wars: The Old Republic: The Bounty Hunter comes across Tarro Blood, his main rival, and the cause of all his problems, in the final leg of [[the Great Hunt]], captured and left to rot in the brig. He requests a last battle to determine who gets to win the Great Hunt. You could do this, or you could leave him there. This sets him off, causing him to pound against the containment field of his prison, screaming about how he's the future of the Mandalorians. This coming from a guy who used dirty tactics, from buying out/killing other competitors, to selling a hit list containing every target's name, but his own, to turning other Mandalorians against a legendary competitor and not honoring a deal. How common was this? This was a Light Side choice, and Wookieepedia regards this as canon, saying that the logical canon route is full Dark side.
In the game based on The Amazing Spider-Man, we find out that Alastair Smythe had escaped custody and, despite Peter wanting to go after him, Gwen keeps him back, reassuring him that everything'll be okay. Then we find out, it's not - he's found out that he's becoming something like the Lizard and he's flipped his lid, activating one of his Slayers and using it to kill himself.
The Prepper from Zombi U, in a rare non-villian example, snaps when the player tries to escape London with the Ravens of Dee and the Panacea vaccine
The Prepper: Oh. I see how it is! You’re all bloody plotting and conspiring behind my back! The Doctor, the Ravens… You know what, fine! Try to save yourself! Die in the fire, for all I care! You’re no survivor, like me! None of you are! You’re nothing to me! Go on, go! Get out! You people are no better than the plague! I gave you shelter, weapons, equipment… I taught you how to survive! You’d be dead without me! And this is how you repay me? You needed me! Oh, you’re all grown up now, strutting off on wild goose chases all by yourself, sticking your neck out…but just remember where I found you! I should have let the Safe House burn, just like the whole of London will! Just like John Dee foretold! No bloody gratitude, that’s the problem with people like you! You just take, take, take, like a selfish child! It’s no wonder the country’s gone to the dogs, is it? Well don’t you worry, because I’ll have the last laugh! I will outlive you all! I thought we were partners! I trusted you, gave you skills and knowledge! I should ***ing kill you myself! GET THE HELL OUT OF MY SAFEHOUSE!
In Injustice: Gods Among Us, Regime!Superman goes into this when the Lex Luthor of his world turns against him and attempts to kill him. When Supes murders Lex on live TV and and he hears everyone's shock and disgust, he flips his lid and decides he's going to bring Metropolis and Gotham to the ground, then bounce over to the mainstream world and do the same there. When Regime!Shazam calls him out on it, Supes grabs him by the neck, freezes his mouth shut and fires his heat vision through his skull.
Shin Super Robot Wars: During the final Space Route scenario, Laodecia starts disbelieving this is happening to him, thinking this is a nightmare he'll wake up from as soon as he returns to the Helmoze...except he can't, because the ship fires its main gun and reduces him to particles.
In Legacy of Kain, the true Big Bad of the series, the Elder God, starts freaking out when it sees that all of its machinations throughout time have spectacularly failed to stop the appearance of the one true threat to its power: the purified Scion of Balance, Kain, wielding the legendary Soul Reaver.
Biara: You have pledged your life to a daughter of Urgash! Ahahaha... You have served me well.
Alaric: *highly panicked* Corrupt the sacred corruption? Yes, Elrath forgives demons that kill demons, Am I a demon? NO! I'm Alaric! High priest of the Light! THE BLOODY RED LIGHT! AHAHAHAHAHA!
Star Trek Online gives us General Hakeev, a Romulan working for the Tal Shiar and especially the Iconians who has been gleefully kidnapping people of all races and experimenting on them. In the mission "The Colosseum", you escape the titular location, find a derelict ship and attempt to contact your ship when Hakeev and other Romulans surround you with Disruptors trained on you. However, when he gives the order to fire, you're rescued just in time, leading him to let out a Big "NO!" is utter frustration. It gets worse in the next mission "Cutting the Cord" when your ship and the Remans lead by Obisek invade Hakeev's Tal Shiar base, running rampant across the place. When you catch up to him, he's begging Empress Sela to just bring the Iconians over now, but Sela has had enough and bails out. Even worse, your final fight with Hakeev is a massive Anticlimax Boss fight he's so far gone. In the end, Obisek (or, if you're playing the Romulan story side, you) put an end to Hakeev's madness by shooting him in the head.
Thot Trel of the Breen missions. He spends the entire mission length trying to figure out the secrets of the Precursors, believing they have incredibly powerful weapons. He's able to take his own copies of the star chart of where the Precursors are and heads into where the source is. However, when both the Player Character and Thot discover the truth, that the starchart leading them to a massive library and a number of cryogenetically frozen Precursors, Thot flips out and demands the entire place dropped on everyone's heads.
In Star Ocean Till The End Of Time, Luther Lansfeld undergoes this. He starts off as a smug chessmaster, having calculated what the party will do and taking countermeasures. When he is finally confronted as the Final Boss, he's undergone major Sanity Slippage, remarking that the party and the inhabitants of the Eternal Sphere are nothing but data and fabrications, and that he, as their creator, has the right to delete everything. He deteriorates yet further after being beaten once, deciding to go ahead and delete the entire universe in his madness. Even in death, he cannot fathom the idea of one's creation surpassing the creator.
In Obsidian, the Bureau Chief, the villainous Obstructive Bureaucrat who has continually insisted on your following the impossible rules of the Bureau Realm, gets so furious from all your rule-breaking that his face even turns into an old stand-by test screen for TVs, then shuts off for a few seconds. And even then, he still is forced to give you information about Max.