Lazlow, a recurring DJ and radio host of Grand Theft Auto, was frst introduced as the put-upon host of the call-in radio show Chatterbox. Later games showcase the breadth of Lazlow's radio career (now spanning 25 years) and reveal him to be an alcoholic fame-seeker, rather than the Only Sane Man he appeared to be in GTAIII. By 2008, Lazlow is middle-aged, divorced, despised by his parents as well as his children, and now ekes out a living as an on-the-street "journalist" in Liberty City, decrying the state of America and insulting passerby. As Lazlow's dialogue is written and voiced by real-life radio host Lazlow Jones, this is a form of Adam Westing.
The titular Mercenaries took a page from this in the sequel. What was once a Power Trio of balanced personalities (Chris the cool customer, Jennifer the conniving money-grubber, and Matthias the pyromaniac) tipped into all three of them behaving like Matthias. ...Who is incidentally featured on the cover.
In Condemned, Ethan Thomas is a nice enough guy, a gifted investigator, but personality-wise, he was never too impolite, despite clearly being under some MAJOR stress. Come the sequel, Ethan's undergone about a year of alcoholism as well as some Jerk Ass power leveling. He curses all the time and is routinely impolite and distrustful towards everyone who tries to help him. This is in fact underlined by the change in his voice actor and character design (he went from an Ambiguously Brown SCU agent wearing a nondescript police uniform, to a rather less ambiguously Caucasian bum in grunge clothes). The personality change is possibly justified by the year of vagrancy and the events of the first game.
It should be noted that in the intro to the sequel, he mercilessly pummels a guy for bumping into him and spilling his drink Granted said man was intentionally trying to goad him into a fight, but still.
Hubert Ozwell from Tales of Graces is regarded to be the king of this trope, and one of the biggest in-series trolls, in the Tales Series fandom. He starts off as a weak, and easily-terrified little boy, but seven years down the line he takes about a million levels in badass due to being adopted into the military-based Ozwell family. When he reunites with his older brother, Hubert reveals that part of the alliance his new nation has with Windol is that they get Lhant, the brothers' homeland, and then Hubert proceeds to Blast Caliber Asbel into next week, exile him from Lhant, blow their mother off when she tries to intervene, and then sets himself up as the one running the shots. The reason for his vitriol, however, is less that he's a military man, and more that he felt he was abandoned by his family in Lhant because they wanted him out of the way. Turns out, Hubert's father wanted to spare him from what was going to happen in Lhant. Throughout the game, Hubert also grows out of it and takes a level in kindness, too.
Saïx from Kingdom Hearts 358/2 Days goes from being the emotionless bastard we all know and love to smack around in Kingdom Hearts II to having his behavior borderline monster proportions in regards to Xion. Many were happy to learn that you get to fight him again near the end of the game. His beat down was much deserved. That's what happens when you talk smack about Xion like that. That's right, Roxas kicks your ass. This is especially true because Isa was a pretty decent guy in Birth By Sleep. The rest of the Org. doesn't really suffer any drastic personality changes beyond losing the ability to truly care about others, yet Isa goes from a stoic but reasonably friendly boy to the cold-blooded Jerkass Saïx.
Some fans have suggested from certain changes in Saix's appearance (the pointed ears, lightened hair color, and perhaps most ominously, yellow eyes) that Isa may have been corrupted by darkness before he turned into a Nobody, which would certainly explain a lot...
Turns out, this is because Saix is slowly turning into a Xehanort clone.
Sora (briefly) gains a level in jerkass in Chain of Memories thanks to Namine screwing around with his memories.
Eric Sparrow from Tony Hawk's Underground went from the Player's friend to the game's antagonist who was taking credit for everything you did.
Ironically, between THUG and THUG 2 he Took a Level in Dumbass and is treated as an incompetent loser in the latter.
Word of God is that this was partly intentional: he and Dana were having relationship difficulties and were apart at the moment, causing him to be a little... grumpy.
World of Warcraft: Garrosh Hellscream went from being an obscure emo kid trying to find his purpose in life to being a disrespectful, belligerent, loudmouthed Jerk Ass.
He suffers it again in Cataclysm, and randomly becomes racist. Despite not discriminating and even being friendly with the player in Nagrand. In short he's a walking Conflict Ball.
At the same time, he also seems to get rid of a few Jerkass elements too, ironically. For instance, while he is one of the major reasons as to why the war between the Alliance and Horde has reemerged, there are things he simply won't stand for. First off, he specifically does not approve of Sylvanas raising the newly dead on the battlefield to replenish the ranks of the Forsaken. He also gets really pissed off when he finds out that one of his commanders has been attacking night elf settlements to kill civilians.
Garrosh will be taking this trope to its logical conclusion in Mists of Pandaria. The final raid dungeon is a siege on Orgrimmar itself by both Alliance and Horde, because everyone is digusted by him dropping the magical equivalent of a WMD on Theramore, killing many known characters, including Rhonin, after killing several Blue Dragons to get the necessary power source for the bomb. Many of the Horde factions are not happy about Hellscream's rule but stay out of fear (trolls, tauren) or greed (goblins). In his speech in Jaina Proudmoore: Tides of War, he doesn't even pretend that the other leaders are his equals and expects them to obey him or die. He wants the Alliance gone and take the lands he believes are rightfuly his (even though orcs are not native to this world). Jaina begs Thralls to take leadership back from Garosh, knowing that many would support him, but Thrall refuses.
This, in turn, has an after effect of Jaina finally taking one herself. She loses her all-loving part and her rage against the Horde goes to extreme Fantastic Racism levels as she tried to flood Orgrimmar with her magic, only to be called out of it by Thrall and Kalegcos. Then when she tried to wind down, she's betrayed again that she initiated the Purge of Dalaran with a glee. She's gone as far as suggesting the assassination of the new Horde after Garrosh is defeated, which would mean the death of Thrall... something that even Varian refused. In other words, while Varian Took a Level in Kindness, Jaina ended up doing the reverse.
Palom was an overeager, boastful, and sort of annoying character in the original Final Fantasy IV, but that was probably excusable on account of him being five years old. In Final Fantasy IV: The After Years, though, he's kind of a dick for no readily apparent reason before softening up some.
Before the FMV games, Admiral Tolwyn, from the Wing Commander games and novels, was a gruff but overall fair person. Starting with WC3, though, he became Admiral Asshole (possibly due to typecasting of Malcolm McDowell, the actor that played him), and continued on to SpaceNazi in WC4. William Forstchen's novelizations of those two games tried to lessen that a bit, but was limited by the game scripts he was writing from.
Taki takes one between Soul Calibur III and IV. She goes from hunting demons and fighting those like Cervantes who want the power of Soul Edge to hunting demons and fighting those affiliated with Soul Edge, fighting ex-villains and people affiliated with Soul Calibur, and fighting good guys or neutral parties who might become affiliated with one of the swords. Nearly every character's story path involves Taki trying to kill them at one point. It's certainly not helped that while she does this she accuses everyone but herself of being evil and delusional and makes some verbal low blows against Siegfried and Ivy.
Within Soul Calibur III's Chronicles of the Sword mode, Abelia, your friendly rival at the start of the story and, slightly later, useful ally, turns full tilt into a Knight Templar halfway through, complete with a costume change and deeper, more aggressive voice bank.
The third game sees the Asari and Salarian Councilors take a few levels in Jerkass (contrast to the Turian Councilor). They, however, are beaten out by Quarian Admiral Han'Gerrel, who power-levels in Jerkass to the point of doing positively insane things in his attempt to wipe out the Geth, including firing on a Geth Dreadnaught while Shepard and Tali are still inside it - and Tali is not just a fellow Admiral, she's also the daughter of one of his oldest friends. He also puts his ships and crews in serious danger to force other Admirals to support his reckless actions, because the alternative is losing the heart of the quarian military. If you fail to broker peace between the Quarians and Geth, he has his ships bullrush the geth fleet. Depending on what choices you made, they either get massacred or complete wipe out the geth.
Renegade Shepard was always a jerk, and took a level in 2, but in Mass Effect 3 it's taken to a whole new level. While their behavior was usually rude, condescending, racist, insulting, and did kill a number of people, it managed to have some funny moments in Mass Effect 1 and Mass Effect 2. In 3 Renegade Shepard is downright evil, causes cold-blooded murder of teammates without remorse, and lacks the humor that Shepard had in previous games. You can even tell from the "Commander Shepardis a Jerk" videos.
It's very easy to forget that Councilor Sparatus wasn't actually that bad at first. Harsh yes, but he was reasonable and actually made some good points. It was only after Shepard became a Spectre that he became the unrepentant asshole everyone remembers.
The Illusive Man was always kind of a prick, but in the third game he moves from being a morally inconvenient supporter, who could be extremely ruthless but was also one of the few to believe you about the whole "Space!Cthulhu is coming to kill us all" thing, to being an active enemy to the survival of galactic civilization whose forces brainwash new recruits, attempt to murder and/or brainwash your old friends, launch raids on human colonies to abduct new troops, attack Grissom Academy to abduct a multitude of young biotics, and run a cross between a concentration camp and a Husk factory beneath a refugee camp, out of a plan to control the Reapers that even a number of his former employees think is flagrantly insane. Eventually, it turns out he's been indoctrinated, so his more heinous actions are the result of the Reapers screwing with his head, and a fair chunk of his former seeming friendliness was a pose put on to manipulate you.
Maggie's father in The Legend of Zelda: The Wind Waker. When you first meet him, he's a pitiable pauper who is distraught over his daughter being kidnapped. But when Maggie comes back with a massive fortune in Skull Necklaces, he turns into a selfishly greedy bastard who won't even let Maggie get letters from her (sort of) love interest.
Ingo from Ocarina of Time. While he was never the friendliest person in the game, he was nothing more than a disgruntled employee who complained about Talon's laziness when Link was a kid. After Ganondorf comes to power, he uses the Evil King's "good" graces to take the ranch for himself, exile Talon to Kakariko Village, and proceeds to generally make life miserable for Malon until Link returns and intervenes.
Yukari in Persona 3. She was genuinely the cutie until FES' "The Answer", where she seems to have gained a sour coating over her usual sugary sweet self.
She doesn't become a jerk ass so much as go through a brief Face-Heel Turn
Zoey in The Passing in Left 4 Dead 2. Compared to her nicer and more open nature in the first game, she becomes outright annoyed and angry with some of the survivors in both teams. The reason for her change of attitude is her trying to cope with the recent death of Bill.
Anders takes several levels before and during Dragon Age II. Being possessed by an increasingly pissed off spirit that had no idea of being nice to begin with and gradually succumbing to it does not help a bit. In Act I, he's a bit grimmer than before, but still kindhearted, snarky, and occasionally goofy. In Act II, he eventually attacks (and kills, unless you stop him) an innocent mage he just saved from templars during a bout of Unstoppable Rage, panics, and retreats into a Heroic BSOD. In Act III, he's become completely paranoid of the rest of the party (except for Hawke and Varric), quick to swing between manic determination and deep melancholy, is completely obsessed with his cause, and some of the party banter implies he might be hallucinating.
The Spirit of Justice itself took a few levels in jerkass when it possessed Anders - it's explicitly stated ingame that it was overwhelmed and corrupted by Anders's anger at what was going on, and back in Dragon Age: Origins, it was actually much more reasonable and willing to listen than it is in the sequel. On top of that, it's hard to tell how much of Anders's behavior is this trope and how much is him just plain hugging the Idiot Ball, given the increasingly horrible and poorly thought out choices he makes as time goes on.
Due to how the personality system works, The player character Hawke can slowly change their personality over time to go from a nice paragon hero type or a funny charming neutral type to an aggressive asshole.
Ema Skye of the Ace Attorney series is introduced as an aspiring forensic investigator, full of useful investigation techniques and eager to meet people in the business. However, eight years later she finds herself in a job she didn't want (detective work) after doing poorly on her forensic investigation exam and her derailed dream definitely takes its toll on her personality. The Ema of Apollo Justice: Ace Attorney is a sour and jaded woman who doesn't offer much help (unless she can use some of her forensic investigation techniques, at which point some of her original personality leaks out).
Cloud does this between Crisis Core, in which he's a shy, brave, and supportive person with really bad self-esteem (with some backstory about him picking fights with the people who bullied him in his hometown), and Final Fantasy VII, in which he's a rude, cocky, reckless and obsessive person who deliberately antagonises his friends Barret and Wedge and does things like taking salary from a slum-dwelling little girl's school money. He's nicer to the girls, but also pretty sexist and won't trust them with anything on their own. He gets a lot nicer after a few hours of play, but he remains vengeance-obsessed and arrogant until his entire persona implodes halfway through the next disk.
In Shin Megami Tensei IV, Lucifer is far, far more cruel and insulting than he's ever been in previous installments. Even Merkabah expresses pity and sympathy for Flynn when he's forced to kill Isabeau in the Law route. In the Chaos route, Lucifer coldly brushes off Isabeau's death as if it was nothing.
While in real life Dudley from Street FighterTook a Level in Kindness between III and IV, IV takes place before III, meaning in the game's chronology Dudley went from being exceedingly polite to acting more snooty and calling opponents "gutter trash" (though he zig-zags back slightly by Third Strike.)
In BioShock Infinite's DLC, Burial at Sea, Elizabeth is much ruder to this version of Booker than she was in Infinite. Turns out that it's deliberate, since you're not playing as Booker, you're playing as an alternate version of Comstock who had taken up the 'Booker' persona.
Tails, inexplicably, does this in Sonic Lost World. The childlike naivete and humility that defined him in previous titles was spontaneously replaced with a smug, self-centered, obnoxious, whiny, and snarky attitude. He had a falling-out with Sonic because he was interested in teaming up with Dr. Eggman to corrale the Deadly Six, even though he was perfectlyfinewith it before! The worst part is that he never owns up to it at the end of the game.
Tomb Raider: Lara Croft, a few times. First, between the second and third games, she goes from killing members of an evil cult who want to destroy the world to killing Military Police, museum guards and homeless all for the sake of finding artefacts. The 'saving the world' part only comes in for the last few levels, and by then the only humans left are on her side. The fourth and fifth games see her infamous snark taken Up to Eleven, making her even less civil in conversation with other people... and then the sixth game sees her running around two European cities, contaminating crime scenes, breaking into the Louvre, killing police and security personnel, and being rude to prostitutes. All to clear her name of one murder.