Assassin's Creed: Revelations Ezio goes berserk when he finds Yusuf's body and launches a full scale assault on Istanbul's arsenal. Only one person is spared.
Splinter Cell: Sam Fisher hits this at the end of mission eight of Conviction, where he learns that Lambert was behind faking his daughter's death in Double Agent, at which point, at least for the rest of the mission, Mark and Executes are free, as in no need to CQC enemies to earn them, there's no need to designate a target (simply moving over them with the cross hair makes them a target), and the meter is up to a max of six at this point.
"Unstoppable Rage" sums up Kratos from the God of War series. Plus, he has an ability named "Rage of the Gods/Titans/Sparta", that makes him more unstoppable.
In Ghost of Sparta, Kratos may have topped himself after seeing Thanatos kill his brother. The man truly becomes rage incarnate at that moment.
Fairly late in Super Robot Wars: Original Generation, the hero's girlfriend is kidnapped by a traitor, and brainwashed into not only attacking him, but also aiming deliberate, emotional attacks at him. The result: His mech becomes nigh-unstoppable for the duration of the battle as he performs a Foe-Tossing Charge towards the traitor.
Partially subverted in that Kyosuke never actually shows any real emotion.
The Kaiser Dragon from Breath of Fire III and IV. If Ryu transforms into this from without some tweaking (in III it was a specific combo of Dragon Genes, in IV it required you to gather the various breath weapons of dragons), he'll kill his allies.
The scene where he unlocks it in IV is particularly noteworthy. After he easily exterminates the army officer who pissed him off to such a degree (by slaughtering a village of innocent civilians and THEN setting an absurdly powerful monster on your team, which Ryu also destroyed), he's STILL angry and ready to kill, quickly turning his sights on another officer (who can only point her gun at him while shaking in terror), getting his only lines in the game by screaming in rage the entire time. The whole scene is decidedly scary, and it takes a Cooldown Hug from Nina to bring him back to normal. As the Cooldown Hug occurs, Fou-lu is driven to rage when his girlfriend is used to fuel a nuke.
This trope is a recurring theme in all five Breath of Fire games. The above covers III and IV.
In Breath of Fire I, the only way to get the "True" ending is for Ryu to unleash his most unstoppable form, an Eleventh Hour Superpower useable only in the final battle, which combines all of his allies into a giant gryphon-like-dragon monstrosity hell-bent for destroying an evil goddess from making all of their lives, along with the entire war-torn world, a living hell. The goddess was also indirectly responsible for Ryu's sister's death, so that may have added some fuel to the fire.
In Breath of Fire II, Ryu's second most powerful dragon form is unlocked during a boss fight where a trusted member of his own tribe is revealed to be working for the villains. After taunting and provoking him, the boss finally pushes Ryu to the next level by enraging him, which he reveals was his goal from the beginning.
Upon reaching the final boss, Ryu and his party are encased in crystal by the final boss. The boss then moves party member to party member, revealing the true intentions for each one following him. He then shatters each party members' crystal, killing them, and then simply floats away, leaving Ryu alone, frozen in crystal. Ryu explodes out of his prison, and in the best cutscene an SNES can muster, charges at top speed after the boss, dodging fireballs and explosions until reaching the boss. He then leaps high into the air, and delivers a mortal wound to the boss (until the boss reveals his true form). In the following fight, Ryu unleashes yet another Eleventh Hour Superpower only useable during the final boss fight.
In Breath of Fire: Dragon Quarter, Ryu is hybridized into a Human/Dragon mix, but it is assumed that a hybrid is far weaker than a full-on dragon (as seen by Odjn, who is little more than a dragon that has been pinned to a wall, possibly for centuries, half his body decayed, but remains alive out of force of will). So when the final boss is a fully resurrected dragon taking aim at his only two friends in the world, Ryu bursts across the other side of the room, getting the dragon's attention. As the boss rears back to fire it's massive breath weapon, Ryu leaps from the balcony he's standing on and fires his own projectile. The two streams of energy collide, and a beam struggle commences. Ryu has a D-Counter, which ranges from 0%-100%. Should it hit 100% at any point in the game, Ryu "dies", no continues, do not collect 200 dollars, etc. During this fight, Ryu is so fueled by his rage and need to protect his friends that he pushes himself far beyond his normal limits. He actually breaks the D-Counter, in-game mechanics, forcing himself to go to roughly 164% before finally being able to overpower the enemy dragon, saving his friends.
Arcueid of Tsukihime most notably loses her cool during another heroine's route, when you turn downher offer to turn you into a vampire and slice her nearly in half. The humiliating, excruciatingly painful, and oh-so-temporarily debilitating injury drives her insane, removing the self-imposed restraints on the majority of her power...
In Arcueid's own route, when she gets cut in half by Roa and dies in Shiki's arms, Shiki goes berserk. Roa is several kinds of Deader than Dead by the time Shiki comes down from it.
Actually, nearly all of the routes have a tendency to end with Shiki falling into this mode. In Akiha's route, after SHIKI hurts Akiha, Shiki completely loses it and goes into his killer mode. Later, in the same route, when SHIKI Mind Rapes Akiha, it takes all of Shiki's willpower to not kill SHIKI immediately. He does kill him, but not before SHIKI tells him how to bring Akiha back to normal. Then, in Hisui's route he goes into a similar homicidal rage when SHIKI either badly wounds or, if it's your first playthrough, kills Akiha and slice him in half in a single stroke. Finally, Kohaku's route features an aversion, when Akiha seems to murder Kohaku in cold blood, Shiki loses any semblance of reason and attempts to kill his own sister. In the end, despite all the wrongs Akiha has committed against Shiki during the course of the route, Shiki still finds himself unable to kill her, realizing that, no matter what she's done to him, she's still his irreplaceable sister. In fact, he even cries when he realizes this. Luckily, as it turns out, Akiha was unable to kill Kohaku either, so all's well that ends well.
Occasionally occurs as a plot device in the Final Fantasy series, often against the villain. Often enough though, the character dies afterwards. An example is Tellah in FF 4.
Edge in Final Fantasy IV as well. It's what unlocks the ability to use his Ninjitsu techniques after Rubicante taunts him about letting his emotions get in the way.
''You think our rage... a weakness? Then let me show you how wrong you are!
Happens before the plot of Drakengard, so the protagonist is in almost a constant state of Unstoppable Rage throughout the game. His rage abates by the time any of the endings roll around, but hey, most of the people are dead anyway.
It doesn't abate for long. Although by the time the sequel comes around, he has a very good reason to be pissed off. You'd probably be mad too if your pact partner was imprisoned and tortured for eighteen years after she voluntarily sacrificed herself to become the new Cosmic Keystone.
The attack Rage was unstoppable in Pokémon Red and Blue, and Yellow, only stopping if the Pokémon using it is switched for another one or has an attack used on it that prevents attacks. However, starting with Gold, Silver, and Crystal, the attack doesn't have to continuously be used, though doing so increases its attack power when the user is attacked.
Similarly, the Dragon-type move Outrage was added in Gold and Silver—the user is locked into Outrage for two or three turns, and can't be recalled unless the attack is cancelled by a move that prevents attacks. Moreover, it was buffed in Pokémon Diamond and Pearl to become one of the most powerful Dragon-type moves available.
There's also Hyper and Reverse Modes in Pokémon Colosseum and XD, respectively. Hyper Mode heightens the critical hit probability for Shadow Rush (which doubles both the damage and the recoil), but makes the Pokemon unlikely to use any other attack. Reverse Mode trades the bonus for a heightened probability to obey another attack command, but the Pokemon in it sustains end-of-round damage for as long as it's in Reverse Mode. In neither mode can healing items be used on the Pokemon in question, and the conditions even persist after treatment at a Pokemon Center! The worst part of all: the closer a Shadow Pokemon is to purification, the more likely it will go into these modes.
Having your Shadow Pokemon go into Hyper Mode is actually a good thing, since snapping them out of it is a fast way of purifying them.
The Anger Point Ability quadruples the user's Attack when struck by a critical hit. The three Pokemon that can have this naturally? Mankey, Primeape, and Tauros, none of whom are known for having very good tempers.
IGN, when revealing the Shamar trailer for Sonic Unleashed, left this caption for it, as well as an icon of the Werehog:
He may not be green, but you won't like him when he's angry.
Alma. She's dead, and her hate is what keeps her present on this mortal coil. One character in F.E.A.R. 2 even says that her hate is the reason she just "refused" death.
At multiple points in Project Origin, Alma attacks and slaughters people without warning in random spats of sheer violent hatred, complete with her distorted voice screaming " I HATE YOU!" over and over again.
In Knights of the Old Republic, both the party member Hanharr and the PC (if you choose the Sith Marauder prestige class) can fly into this. While Hanharr has to eat the defense penalties involved with a rage, the PC at endgame is generally more or less immune to ranged fire.
It's worth noting that in his Wookie Fury, Hanharr can tear through even Dark Jedi without taking any significant damage.
At the end of the Marine campaign in Call of Duty: World at War, if you let Sergeant Roebuck die, Private Polonsky will go mad with rage at the Japanese. Also a cross between Cutscene Power to the Max and an Informed Ability; his emotional state is clear from his spoken lines, but his behavior as a friendly NPC in terms of game mechanics stays the same.
On the opposite side of the morality scale, we have Raul Menendez in Call of Duty: Black Ops II, who, upon being torn away from his sister, Josefina, goes into a blind rage. This mad dash comes complete with anime rush streaks when sprinting, superhuman bullet-sponge-osity, and the ability to "reload" his shotgun simply by throwing it away and picking another one up from the dead soldiers he just killed, all in the space of two seconds. And yes, it is as much fun to play as I made it sound just now.
In the Halo series, Ultra Elites and Brutes will berserk and rush you with deadly melee attacks if the rest of their squad is wiped out, or if they are pissed off enough(eg from being stuck with a plasma grenade). In Halo 3, Grunts will "kamikaze" with plasma grenades in desperate times.
When its "blood brother" is killed, the other Hunter will immediately attack whatever enemy who stands in its way, attacking them like an enraged elephant without using the arm cannon, just its shield swinging it like a bat.
In Left 4 Dead, the Tank special infected is the literal embodiment of this trope. The second the Tank sees you, it will not stop attacking you unless all the survivors are dead or incapacitated, it's dead, you get out of sight and don't get hit for upwards of sixty seconds, or you get into the ending safe room. In the case of getting out of sight, the tank dies due to frustration. Oh, and don't try hiding in the beginning safe room. It will bust the door down and beat the everloving crap out of you.
Tony Montana in Scarface: The World is Yours has turned his mercurial temperament into a Limit Break the game calls Blind Rage. Starting off from the climactic shootout at his mansion which serves as a junction point for the game's Alternate Universe premise Tony can build machismo and brashness (in increments measured in Balls) until the Charge Meter tops out, at which point he can break out into his trademark burst of obscenity-spewing rampage where not only he can autotarget enemies For Massive Damage with any weapon or even his fists, but every enemy killed during the Blind Rage results in a partial restoration of Tony's health. Tony can increase not only his incremental Ball gains, but also the duration of the Blind Rage throughout the game.
The instruction booklet put it best, "Nobody flips the fuck out like Tony Montana".
In Baldur's Gate 2, hulking, amiably insane ranger Minsc is desolate over the loss of Dynaheir, the witch he swore to protect. Then, if you allow Aerie to join your party, he forms a similar attachment to her and offers to protect her with his life.
He also has a berserker rage option in combat. It can be a problem, because he regularly just wigs out and forgets who's a member of the party and who's not. He does, however, get points for shouting "I will inspire you by CHARGING BLINDLY ON!"
Meta Knight had one of these moments during the "Revenge of Meta Knight" Mini game in Kirby Superstar. At the end, during the final escape scene, Meta Knight enters by shouting "YOU WILL NOT ESCAPE!" and than proceeds to chase you hurling swords at you at every chance he has.
Also, the Daedra Lords should you fail one of their quests, especially if you choose not to return Umbra to Clavicus Vile.
In the Shivering Islands, Sheogorath has a few of these, though they are mostly funny.
Though you don't see it, Falcar supposedly had one before leaving the Mages Guild in Cheydenhal.
Somewhat used for Don Flamenco in the Wii version of Punch-Out!!. When you knock his toupee off his head, he will get so pissed that he will constantly throw punches at you until he goes down, you go down, or if the round ends.
"You really do remember me this time? I'm soooo FLATTERED!" (Cue flames rising, weapons appearing out of nowhere, and a scary guy with red, spiky hair giving you a Slasher Smile) "But you're TOO LATE!"
"You both...think you can do whatever you want...Well, I'm sick of it. Go on, you just keep running. But I'll always be there to BRING YOU BACK!"
When its seemed that Goofy died, Sora, Donald, and King Mickey immediately attacked The Heartless horde with much more ferocity. The rages of Donald and the King was clear, such as Mickey saying "They'll pay for this" and then rushed right at the horde with his keyblade at his hand, with Donald and Sora right behind him, and they curb-stomped at least 1000 heartless each.
Then there's Terra's. It reanimated his armour just to fight the guy who had possessed him and the musical theme accompanying this battle? Its (very fittingly) called Rage Awakened.
Played straight in World of Warcraft, whose Warrior and Druid(bear-form) classes require a constant supply of Rage to fuel their attacks.
Likewise with the Hunter talent, Bestial Wrath, which causes the Hunter's pet to do this (Again, without feeling "pity or remorse or fear"). A further talent allows the Hunter himself to share the rage.
Even straighter in Runes Of Magic, where warrior classes use Rage energy to attack, have a self buff increasing how fast they become enraged, potions also increasing rage, a straight up rage button, and two abilities that are essentially "I'm pissed so I'm going to hit you harder now." buttons.
In Watchmen: The End Is Nigh Rorschach has a literal Rage meter that fills the more bad guys you pound and gives you special, extra-brutal attacks.
This is what happened to Mother Brain at the end of Super Metroid.
In the Rome: Total War expansion pack, Barbarian Invasion, some barbarian factions make use of berserker units who possess the special ability to enter an Unstoppable Rage.
Panicked war elephants and chariots may also qualify for this.
Hopeleslly surrounded units may choose to "fight to the death" rather than flee.
While very short, Junpei's Persona evolution in Persona 3 very much qualifies, as he Screams in rage at Takaya killing Chidori, summons Hermes which subsequently evolves into Trismegistus for all to see, and blasts Jin off his feet, showing that he'd quite happily rip them both limb from limb if his friends didn't talk him down. This is even more notable by way of remembering the rules of fighting in the game: Junpei used Agidyne, a fire spell he could not actually possibly have learned at that point, and the sheer power of his burning passion allows it to knock down an enemy previously noted in-battle as being immune to fire.
In American McGee's Alice, Alice can find Rage Boxes, which represent her anger over the death of her family; if she uses one, she howls in pain, her skin turns blood red, horns grow on her forehead, spurs grow from her back, and her hands turn into horrid claws - for a limited time. In game terms, this is a Power-Up that makes Alice do more damage to enemies, and requires her to spend less mana points for her attacks. (Most of the time, there's only one Rage Box per level, and sometimes there is none; the player can save them for when they are needed.)
Diablo 2 has the barbarian's "frenzy" attack, causing the character to attack and run faster and faster as they attack enemies.
The Diablo III Barbarian has Wrath of the Berserker, essentially a Super Mode for the character that allows him or her to attack faster and harder.
Alex Mercer is in this state for at least a quarter of the game.
"NOTHING CAN PROTECT YOU FROM ME! NOT MEN! NOT WEAPONS! NOT ARMOR!"
"DIG IN! LIKE IT'S GOING TO MAKE A DIFFERENCE!"
Heller has one in in the sequelwhen assaulting the Gentek HQ to get back his daughter. He was capable to force two Juggernauts to his aid and his damage output is dramatically increased to the point of being able to kill Orion soldiers and Brawlers in one hit.
Ragna the Bloodedge: Got his sister kidnapped, his brother brainwashed and his arm torn off. Response? Annihilate the world government and slaughter every single individual associated with it. By the way, this guy is supposed to be the hero of the game.
Noel Vermillon: Don't ever, EVER mention her lack of "assets". If you're lucky, she'll put you under arrest. If you're less lucky, she'll put those guns of hers to good use and some bullets in your head.
Jin Kisaragi: Don't be Noel Vermillon. Just don't. It's a commonly agreed upon fact that it's not a very good idea to be her in his presence. Also, hurt Tsubaki in front of him if you want a cold, slow, painful death.
Hakumen: Never EVER so much as scratch Tsubaki in front of him. If you do, he goes from being fueled by justice to complete and utter hatred. Too bad this causes his downfall in his Continuum Shift bad ending.
Kokonoe: Terumi is a berserk button by simply existing. He not only knows this, but he constantly provokes her by reminding her of her mother and that he killed her. If he so much as says her name she'll give Tager (or Lambda depending on who's there) a good old fashioned "Kill that son of a bitch!!!" order.
Valkenhayn: Don't insult, threaten, or (god forbid) hurt Rachel. Insults irritate him, threats make him hostile, and hurting her will have him in your face in no time flat.
Hazama: Normally, he's the one trying to draw this reaction from you. But if you give him the idea you're toying with him, he'll skip to killing you. And if you have any knowledge the containment of which is vital to his plot, well...
Restriction 666 released! Dimensional interference forcefield deployed! *laugh* I'll show you the true power of the Azure! Code: S.O.L.! BlazBlue, activate! Let's go, you little bitch!
Silent Hill 3's Heather, who is normally a clean-mouthed and calm person, does this near the end of the game to Claudia Wolf in a fit of pure rage before she begin to birth the goddess.
"SHUT YOUR STINKING MOUTH, BITCH!"
Dwarfs in Dwarf Fortress get a double dose. If they get annoyed enough (by bad weather, friends' deaths, swarms of flies, etc.) without enough to make them happy (well-cooked meals, talking with friends, cute pets) they go on "tantrums" where they randomly attack other dwarfs, break furniture, or pull levers until they calm down from the catharsis, and hopefully before they provoke another dwarf into a tantrum. In combat, they can occasionally go into a "martial trance" that significantly boosts all their offensive and defensive combat skills.
It goes further. One step up from "tantrum" is "berserk rage", which will make your dwarves really fuck shit up. As in killing other dwarves, breaking workshops, hitting levers and all that until either the military or the fortress guard take them down (usually, the take-down is permanent...). The phenomenon known as "martial trance" is more like Tranquil Fury, all things considered. The OTHER kind of rage status in combat, simply called "enraged", is triggered when a dwarf in the squad (or a dog) dies. At least one if not a few dwarves around the recently deceased will do some kind of acrobatic somersault off the handle - but this time, those tiny drunken sociopaths target the enemy. Splattering ensues. One user set the probability for dwarfs to enrage extremely high. Then, he let three dwarfs storm onto two trolls. The speardwarf enraged, ran to them, beheaded one (WITH A SPEAR) and killed the other with a stab through the heart before the other two dwarfs even reached him.
Asura goes from "pissed off" to "pissed off enough to punch a planet-sized Buddha to death" to "pissed off enough to not care that my arms have shattered" to "pissed off to the point that I'm indiscriminately firing nuclear-scale explosions into space."
Of note, however, is that in spite of Asura's wrath being a terrifying and unstoppable force, he is at the same time not a mindless force. Even when completely lost within his own sheer, violent, supreme hatred, Asura still refrains from harming innocents and noncombatants. But anything he perceives as an enemy — such as the Gohma or the Seven Deities and their soldiers — are targets.
Grolla Seyfarth of RosenkreuzStilette is generally calm and collected and is every bit as strict with others as she is with herself. But what happens if you hit her Berserk Button in any way? Cue Unstoppable Rage. She'll go on a Roaring Rampage of Revenge and won't stop until she finally has her revenge.
Rink Refraktia's generally lively and outgoing, but if you hit her Berserk Button by messing with her older sister Lecht, she'll stop at nothing to remove you as a threat.
Tryndamere in League of Legends has the ultimate ability Undying Rage, which makes him temporarily impossibly to kill and cannot be prevented from being cast.
Olaf played right is this. His ultimate removes crowd-control effects as well as making him immune to crowd-control effects and reduces damage taken for its duration, his passive increases attack speed for the % of health his is missing, and another choice ability to this in one which increases his damage and gives him Life Drain based off damage he does for a duration. Timed right, he will be a unstoppable and furious attacker where attempts to kill him just cause him to do more damage due to him not hitting Critical Existence Failure. Timed wrong, well... it probably won't be worth the try.
And then there is Renekton, who at this point feels nothing but rage.
In Star Wars: The Force Unleashed II, Starkiller experiences this when Darth Vader shoves his Love Interest Juno Eclipse out a window. It begins with Starkiller going into perpetual Force Fury note it is only cosmetic, attacking Vader with all his might screaming that he will kill him, and ends with Starkiller saturating his foe with lightning for two minutes straight.
Ever fight the Fire King in Odin Sphere? He fits this to a tea. What sets him off is not being able to make Gwen love him and the end of the world prediction that his rage actually sends him into playing his role in it to end up being stopped by the world tree. He takes entire kingdoms down in his rage.
Bakumi Moriyama of Crimsoness. And when one bad day sets her off, everyone will pay.
After Handsome Jack kills Bloodwing in Borderlands 2, Mordecai flat out loses it. Complete with blood-curdling yells of rage, and annihilating a group of bots Jack sent after you, in about 10 seconds.
The Goliath class of enemies are made of this. They're basically just giant mutated bandits who seem tame enough...until someone shoots off their mask. Do this and they will drop their guns and reveal their hideous shrunken head, then get mad and go on a bare-fisted murder spree against everyone in the area (friends and enemies) until they die. They can even level up and become stronger by killing off their fellow bandits, with an instant health refill to boot.
The Fleshpound in Killing Floor looks like a Giant Mook with rotating maces for arms at first. If you inflict enough damage to trigger it, the medical pump on his chest will turn red. What does that mean ? That means he runs twice as fast and will pummel anything between him and the player who pusehd him. With gory results.
Technically occurs in Vampire: The Masquerade - Bloodlines. If you lose too much humanity you may go into frenzy mode. On one hand, it makes you nigh unstoppable, boosting your skills and power exponentially. On the other hand, it's exactly as one would describe a "frenzy"; you don't control the character until it's over and will likely have lost most (if not all) Masquerade points from running around biting everyone, meaning powerful vampire hunters will be attacking your now-weakened form.
Here's a sick wrinkle to Rage Mode in Dead Island. Rather than turn the survivors into a zombie, the kuru virus makes this a game mechanic. Usually it can be triggered at will, but a couple of times they have no control over it and it forces them into an Unstoppable Rage, leaving them freaked upon recovering and seeing the massacre they were responsible for.