"[...] ...as for Imhotep, he was condemned to endure the Hom Dai, the worst of all ancient curses. One so horrible had never been done before. He was to remain sealed inside his sarcophagus, the undead for all eternity. The Medjai would never allow him to be released. For he would arise a walking disease, a plague upon mankind, an unholy flesh-eater with the strength of the ages, power over the sands, and the glory of invincibility!"
A long time ago, the Punishment committed a terrible crime. It was decided that the only way to truly make him pay for his deeds was a torture of the darkest supernatural sort. A side-effect to this, however, would be the punished one becoming immortal and/or gaining control of the forces of life/death/darkness itself. The Punishment then uses this new power to bring terror and death to everyone.
Which may prompt the audience to wonder "Wait... they're giving him magic powers and immortality as a punishment?! Is this Cursed with Awesome or not?" The answer, is, of course, "Yes." So now the punishers must face a supernatural being, in as much pain as possible, who hates them even more than before. Good move, geniuses. They now have to keep them locked away somehow, but this usually doesn't bite them in the ass. At least, not them. No... it's the present generation's problem. More often than not, the result of a Neglectful Precursor's bad parenting. If you're lucky, there will be an Achilles' Heel that can break the Punishment.
Of course, even with great power it's still implied that it hurts. It's sometimes more a punishment to humanity for having allowed such a person to exist. Or, the punisher just doesn't care what kind of threat they would become if free... just as long as the Punishment is in as much pain as possible.
Unishment, where the intended "punishment" is actually something the character enjoys or wanted all along.
In the series Hell Girl, Enma Ai is cursed for taking violent revenge on the townspeople who killed her. Her punishment: to become the Hell Girl, bringer of revenge. She offers a service for people with bitter grudges they can't do anything about. She'll take the hated target to hell immediately; in exchange, the contractor will also go to hell upon dying. Thus Ai's "punishment" is a much greater punishment to mankind — her service keeps the vengeance and bitterness flowing.
That was kind of the point - it's implied that her employer is the Devil.
She can only use her powers to avenge others; if she tries to send someone to hell without making a deal with someone else (like when she figured out that annoying reporter and his daughter were descendants of her cousin) she is sent to hell instead.
The curse of The Buzzard, from The Goon, falls somewhere under this. The Zombie Priest, a powerful necromancer and implied demonic entity, cursed a Wild West sheriff to become an "Anti Zombie", an immortal being compelled to feast on the flesh of corpses and the undead, while still remaining alive and thus effectively beyond his control. He performed the magic to transform him into a zombie, but in a panic because The Buzzard was about to shoot him he messed it up. In doing so created his own worst enemy: a zombie-fighter who will never age, never die, can't become one of the undead, and eats both the zombies he kills and the corpses that the Zombie Priest needs to make replacement zombies.
In Generation X, Penance was an example of the punishment. For teasing him, Emplate used black magic to trap his sister Monet in the Penance body, a red, spiny haired, long clawed, hard as diamond, erratic moving body. The Penance form also made it almost impossible for her to speak and her skin was sharp enough to cut through materials like pants and human flesh, this with claws replacing fingers made it hard to interact with anything. She was locked away andperiodically fed onby Emplate, the idea being if she ever escaped, she'd find no love from the world as long as she was in the Penance body. Pretty slick, too bad she broke out and got love from Generation X.
The Wendigo from Marvel Comics, itself based on Native American myths; according to the folklore, those who resorted to cannibalism in times of famine would be transformed into giants with hearts made of ice and an insatiable desire for human flesh.
Superman-Prime: At the end of his first storyline as antagonist, he was imprisoned within the main Green Lantern battery by the Guardians Of Oa, themselves. Not only does he escape in short order, but his method of escape (absorbing enough of the battery's energy to break free) temporarily left him with supercharged power levels - strong enough to fly between dimensions, destroy planets on a whim and slap around Mr. Mxyzptlk.
Being Neglectful Precursors of the highest order, this wasn't even the first time the Guardians of Oa had tried The Punishment and seen it blow up in their faces. They once imprisoned Sinestro in the central power battery, forgetting they'd already stuck the living personification of fear inside there - which Sinestro quickly awakened. The resulting clusterfuck ended up killing all but one of the Guardians, reducing the number of Green Lanterns in existence from 3,600 to 1, and technically destroyed the universe. The lesson: the Can you Seal Evil In and the Cosmic Keystone that is the very heart of your power should be two different things.
Penance (different Penance) used to be Speedball, a Fun Personified character you've probably seen elsewhere on TV Tropes, until he caused a major accident resulting in multiple deaths, so he inflicts this upon himself. No one really got it. He's been restored to being Speedball, though the survivor's guilt that fueled his Penance persona is still there.
The comic book Chakan The Forever Man (which inspired an obscure Sega Genesis game) is about the eponymous Chakan, a master swordsman, beating Death in a swordfight in order to gain immortality. He becomes immortal; however, for his arrogance Death curses him with a zombie-like visage and "eyes that burn with hellfire", and also to be constantly tormented by nightmares where "pain is real and unforgiving". If he can destroy some Eldritch Abominations, though, Death will finally let him rest forever.
Vampirism in the Marvel Universe was a cabal of Atlantean sorcerers' attempt to punish their foes with a Fate Worse than Death using a spell from the Darkhold. It backfired, like most spells from the Darkhold. The first vampire, Varnae, was very powerful. Fortunately, he eventually grew weary of his existence and immolated himself in sunlight...but not before passing on most of his power to a fledgling Dracula.
Superman II: General Zod and his henchmen are a variation. The Phantom Zone renders them immortal, and eventually it indirectly gave them powers by drifting too close to the yellow sun (and a convenient nuclear explosion).
Although he's not shown to be suffering, the Big Bad of Dungeons & Dragons: Wrath of the Dragon God tells us that he's suffering the pain of undeath until he finds the orb which lets him control the title dragon in the opening sequence, and so he hunts it down, causing the rest of the story to happen. Even as a great wizard, that he is shown to be, it doesn't cancel out the pain. When the main character's wife falls under the same curse, it is seen as painful, along with the implication that when she first begins to turn all of the mages she's working with will turn against her.
The Oathbreakers from Lord of the Rings are an example of the Punishment done smartly- they get undead immortality as part of the curse for betraying Isildur, but become bound to serve his descendants if they ever need to call on them, and the only real power they get is the ability to inspire unnatural terror (shared by all Middle-earth undead). This is also a true punishment, as in Middle-earth the mortal soul wants to leave the world after the span of a lifetime and is in agony if it cannot.
The Mummy Trilogy: The eponymous mummy. Particularly bad Fridge Logic too, because the people who cursed him in the first place had to spend the rest of their lives guarding him, as well as pass that on to all their future generations. Meanwhile, the title character attains immortality, has enough power to bring about The End of the World as We Know It, and can essentially try as many times as he wants to bring his former lover back from the dead. In other words, the mummy was Cursed with Awesome and his punishers got nothing out of the deal to make it worth it.
The film does provide something of a justification that the curse was feared by those who might use it since the mummy's resurrection would allow him to use incredible power, but it would cause the cursed one to experiencehorrifictorment in the afterlife. The fact that it starts off with being mummified and sealed alive in a casket with flesh eating insects, with the implication that it gets worse from there, may make the powers granted an odd form of Equivalent Exchange.
Captain Barbossa & his crew from Pirates of the Caribbean: Curse of the Black Pearl stole cursed gold and were turned into a literal "skeleton crew" because of it. While they could not get any pleasure from anything, they ended up being far more formidable foes, as they couldn't be killed.
It's heavily implied that they get hungrier and thirstier with each passing moment—in other words, they are starving as if they haven't eaten in decades, but they can't die. Besides, by the time the gold was cursed, the Aztecs were dead. The gods probably didn't care what happened to the rest of the world.
Jack actually catches on to this and gets himself cursed just long enough to survive the fight against Barbossa.
Davy Jones and his crew from the second Pirates film suffer under similar circumstances, but in their case (his, at least) it's out of choice. It's also explained that over time they lose their identity, and as a result the crew are little more than puppets of their corrupt captain's malignant will. In the third movie Will Turner becomes the new captain of the Flying Dutchman. Since their new captain is willing to perform his duties as a psychopomp, the crew's humanity is restored.
In the Hercules: The Legendary Journeys movie Hercules In The Maze Of The Minotaur, Zeus punished one of his evil sons by turning him into a minotaur and trapping him in a tomb for 100 years. The idea was that the son would be humbled, because he was very vain and the minotaur form was ugly. After he frees himself, the minotaur mocks the idea that the experience would humble him, and continues his evil ways. The minotaur form makes him strong enough to fight Hercules.
Warrior-king Lo Pan from Big Trouble in Little China was defeated by the first sovereign emperor of China and afflicted with the "curse of no flesh" making him immortal and indestructible, albeit without physical form.
In The Dresden Files second book, "Fool Moon", there is a character who is under a hereditary curse that turns him into a massive, Chaotic Evil, unstoppable, berserk super-werewolf during the full moon. He doesn't enjoy it but it's a lot worse for everybody else.
To put this in perspective, at one point the character is arrested and thrown into a holding cell, hours before a full moon. The result is a level of devastation that makes the rampage in the police station scene from The Terminator look positively tame by comparison.
A common punishment in Perdido Street Station is to replace parts of a person with mechanical or biological parts, which are always at least inconvenient. But more often completely dehumanizing, crippling, and horrible. Sometimes, as with Jack Half-A-Prayer, they provide an advantage that the judges who imposed the sentence never thought of, making the "reMade" a more dangerous criminal. Since they tend to also be assigned to hard labor, some are given mechanical strength enhancements in order to make them more useful, which also has unfortunate side effects if they get free.
The Death Knight Lord Soth from the Dragonlance books. He was given a holy quest to stop The Cataclysm, but turned away from it to confront his wife, whom he suspected of cheating on him, and then refused to save her when she died in The Cataclysm. For this, he was cursed... with immortality, nigh-invulnerability, and incredible magic power, and the 13 knights that served him were likewise transformed into undead creatures under his control.
One has to consider that this moment of failure made the unlife of Soth a mockery of all he stood for. Yes he gained power, but never would he know peace.
The Word of God says that he got immortality and eternal agony from the gods of good that would remain until he would beg for forgiveness, but the awesome magical powers came from Takhisis, the Queen of Darkness who wanted to use his hatred for her own purposes. He refused to listen to both parties, instead content to sit in his castle and think of his past mistakes until Kitiara came along and showed enough bravery to intrigue him.
Later in the series, we see scenes from the perspective of other undead characters Palin and Dalamar, who are in agony because they can eternally see paradise but never reach it. In the very likely possibility that Soth suffers something similar, his incredible powers probably just seem like a bad joke compared to what's perpetually being dangled just out of reach.
Soth may be an aversion in the very end, depending on who you believe. According to Dragon Magazine in its list of top D&D villains, Soth was indeed transferred to Ravenloft, and ruled his own dimension for a time...and eventually, the torment of that plane (and possibly interaction with a magic mirror of some sort?) got to him, and pushed him into an epiphany. When Takhisis came calling again, Soth rejected her. She slew him, and he finally found peace.
It's worth noting that, while the 'Punishment' was a rousing success with Soth, various Dragon Lance gods try it later in the series. It does not work. At all.
Specifically, Soth in life greatly valued his identity as a Knight in Shining Armor, so being turned into an undead parody of one was legitimately hellish for him. However, when Ausric Krell (a thuggish, backstabbing Smug Snake) is punished in the same way, he quickly decides that being an immortal Magic Knight more than makes up for the drawbacks of undeath in his book. So it's definitely a case where one punishment doesn't fit all.
Prince Gaynor the Damned from Michael Moorcock's multiverse. It was less Cursed with Awesome than many of the examples, since he was obviously consumed by despair and misery. He did get the "control over the forces of darkness" bit, but doesn't seem to take much consolation in it.
Nikolai Gogol's short story A Terrible Vengeance tells about the horror a warlock unleashes upon his family and neighbours. Nothing can stop him, Everybody Dies, then a nameless new character pushes him off a cliff. The last chapter explains his seeming invulnerability. A traitor's bloodline was cursed to produce an extremely evil man, who will be committing evil deeds for many decades until cast into abyss by the man betrayed and killed by his ancestor. The purpose is to torment the traitor stuck in his grave and unable to hurt his disgraceful descendant. Other warlock's ancestors suffered while he was alive, but now that he's in hell they'll be tearing him for eternity. Only the traitor still can't join them and will suffer eternally. Also the betrayed one is forced to watch as a punishment for inventing such a monstrous vengeance.
Live Action TV
Buffy backstory: For over 100 years, the vampire Angelus was a heartless killing machine. When he finally chose the wrong victim, a young gypsy girl, her tribe took swift revenge: they cursed him with a soul that felt the torment and guilt of all his sins. That much was a good idea. To twist the knife a bit more, the curse was designed to end if the newly moral Angel felt a moment of pure happiness. That wasn't a bad idea either, as it meant that if having a soul ever became a good thing for him, he'd lose it. No, the bad idea was not telling Angel that! Unaware of the "escape clause", Angel had that happy moment, and Angelus was unleashed on the world again.
Of course, if they'd told him, he'd probably have sought that out. By the time he was with Buffy, he wanted to keep his soul, but he spent quite awhile trying to make it work with Darla despite his soul.
And, of course, Darla, Drusilla and Spike killed them all almost immediately after they cursed him. They only had a brief period to get the information across, and the man who did it seemed to be busy gloating.
Stargate SG-1 backstory: To punish Anubis for tricking Oma Desala into ascending him, the Ancients partially descended him, allowing him to keep some but not all of the Ancient knowledge. The latter was punished by allowing him to wander free so she could witness the destructive power she gave him. She ended this by eventually taking matters into their own hands and fighting the former in eternal battle.
This is one of the central plot mechanics of Reaper. When a soul in Hell is tortured with an elemental force of nature for even as little as two years, if that soul then escapes from Hell, then it will have total command of that element on Earth (and, being a bad enough dude to be sent to Hell and a bad enough dude to be able to escape it, will employ that elemental control with great sociopathic intent).
This was also the mechanic of Brimstone, a series that did the Hell's bounty hunter thing years before Reaper. The longer a soul spends in Hell, the more Hell becomes a part of them; the more Hell becomes a part of them, the more unholy power they're able to unleash when they break free.
Things get pretty bad when someone escapes who had been in hell for several thousand years.
Older Than Feudalism: In Greek Mythology, some versions of the Medusa myth say she was originally a beautiful nymph. Her monstrous form, complete with killing everybody who looked at her, was the result of a curse put on her by Athena, for the offense of sexually defiling her temple. (Although this may be unfair: some stories say she was raped.)
The ancient Indian epic Ramayana features a semi-godly woman who has been punished by being transformed into a demon, which gives her the power to turn the land around her into a burning desert. Her sons meet the same fate, but they already had supernatural powers before their punishment.
The Mexican folk tale of La Llorona. She was a woman who drowned her two children for varying reasons (to get a husband, to spite her ex, because she didn't want them-always a petty and/or spiteful reason). After she died, for some reason God cursed her to wander eternally looking for her children instead of just sending her to Hell. She now wanders the riverbanks looking for her children, and drowns any children she finds to try and replace them. Nice job breaking it, God.
In Vampire: The Masquerade, God punished Caine for killing Abel by turning him into a vampire and cursing him. Now, humanity is plagued by legions of the literally damned undead, which have magic powers, eat people, and secretly pull the strings of many political and financial institutions. Great.
Somewhat ameliorated in the Time of Judgment book "Gehenna". In the first scenario, God decides humanity's carried this burden on their own long enough and takes direct action against all vampires.
The Ravenloft D&D campaign setting runs on, lives, breathes, and eats this trope. An ethereal demiplane dedicated to the punishment of the wicked, its darklords simultaneously are granted great power over their domains and subjects, but are denied their greatest desire. Examples include:
Strahd von Zarovich. In life he was a warrior who spent over 20 years fighting to free his homeland from foreign invaders. Suffering over a youth spent in battle, he eventually fell in love with his younger brother's fiance, Tatyana. On the eve of their wedding, Strahd makes a pact with a monster to gain everlasting life and Tatyana's love. He is transformed into a vampire and murders his brother to have her. At the same time, a Gambit Roulette by a rival lord kills off most of Strahd's retainers. During the ensuing battle, Tatyana leaps over the castle ramparts in despair over her dead love. Since then, Strahd has enjoyed everlasting life and absolute control over his homeland, though every generation, Tatyana is reborn among the populace, where she inevitably attracts Strahd's attention, is courted for a brief period, and is killed in some gruesome fashion without fail.
Azalin Rex. A wizard king from the Greyhawk setting, he ruled his land with an iron fist. He fathered one son, who spent his childhood having the kindness beaten out of him so that he could become Azalin's ideal successor. This failed, and Azalin executed his own son when he was caught to smuggle condemned prisoners beyond his father's reach. Azalin made a similar pact as Strahd to learn the process to become a lich in order to gain immortality to rule his land forevermore. Decades later, he learned of a scroll containing a spell to resurrect his dead son. At the same time, he was cursed with being unable to learn new magic. Thus, he has the means to correct his greatest "failure", but cannot take advantage of it. Even worse, his new castle in his new domain has a room that would let him circumvent his curse, but every instant in the room causes him agonizing pain, as his undead body is brought back to life, cell by cell, basically decaying in reverse. So in the end, he is the absolute and immortal ruler of a vast kingdom, but can never improve himself or hand his responsibility elsewhere; he can't move up and he can't move out.
Lord Soth, described above, had the chance to prevent a world-shattering cataclysm but did not do so out of pride and jealousy. Since then, he had spent the next three hundred years listening to his banshee servants sing the songs of his failures. Eventually, he was transported into Ravenloft and given an exact copy of his former castle, perfect in every detail... Except the architecture keeps changing, which drives Soth - accustomed to rigid military order - crazy.
It's interesting to note, though, that out of all Dark Lords, Soth's Punishment in "Ravenloft" was barely worse than what he already suffered in his native setting of "Dragonlance". That's probably why he was sent back to Krynn (the world of "Dragonlance"), from both an in-story perspective (his torment probably wasn't satisfying enough for the Mists) and from a meta perspective (he really wasn't that interesting as a Dark Lord).
Vlad Drakov, a Canon Immigrant from the Dragonlance setting, spent his free time as a mercenary general who won many wars but was constantly looked down upon by his clients as he yearned for a country to call his own. Ravenloft provided in its own unique fashion, giving him a domain fashioned in a fascist dictatorship centered around a permanent police state and military government. Drakov was delighted at first, until he discovered that for all his new status, his new country was a backwater tract of mud surrounded on all sides by more advanced and prosperous domains. Which he tried to invade. Over and over and over again, each defeat replacing more of his reputation as a ruthless if successful general with one as a bumbling idiot.
Vecna, a demigod from the Greyhawk setting, was trapped by the Dark Powers by virtue of him tying too much of his power into his avatar. Being a god and all, there isn't really much the Dark Powers can do to curse him other than hold him in place and tie him into a physical form, which in a way is punishment enough. Vecna's domain is one where he has won completely, with undead holding all the honored places in society with living mortals as a permanent underclass, but the domain itself is a bare spit of land and Vecna knows the longer he remains, the more damage is done to his cause back on Oerth, which is where he wants his "real" victory. Eventually he goes into full Gambit Roulette mode and escapes, but nobody ever said the Dark Powers were perfect.
How about Jacqueline Renier, a wererat who clawed her way into power? Her curse is twofold: First, she suffers from intense monophobia, which makes her prefer to keep her family (who HATE her) around rather than spend even a moment alone... Secondly, she is doomed to transform whenever she is in the presence of someone she loves. So, essentially, she wants love and companionship more than anything else but is unable to get it...
Or Dominic D'Honaire. He was an exceptionally manipulative child, who frequently stirred up trouble among the adults around him for his own entertainment, yet always managed to evade suspicion. He was doted on intensely by the women in his life, in large part because his mother died giving birth to him. As a darklord, he now has the power to control the minds of anyone, making anyone adore him... Except for women whom he is attracted to, who are immune to his control and start seeing him as progressively more repellent.
Pharaoh Anhktepot, Ravenloft's token mummy darklord, suffered the Punishment twice. First, Ra punished him for his hubris by making his touch lethal, so he started killing his own subjects until the survivors murdered him. Then the Dark Powers got wind of his misdeeds, and confined this once-mighty king in a tiny domain with just a few hundred inhabitants; now undead, Anhktepot can become alive for a day by sacrificing one of its residents, but he knows that doing so too often means he'll run out of subjects and be alone forever.
Alfred Timothy was the neglected son of Nathan Timothy, himself a former Darklord. Puny and weak, he was scorned by his father and eventually fell in with a cult worshipping a Wolf nature god hoping to gain enough strength and confidence to be accepted by his father as an equal. Eventually he succeeded and was transformed into a full-fledged werewolf, with the power to tear his enemies to shreds and command respect from his lessers. He was then cursed to transform back to human form if he ever lost control of his emotions. He would love nothing more than to give in to his bloodlust and kill and rape at will, but even as a monstrous beast he is forced to be careful and dispassionate in all things lest he reveal himself as a weakling and be himself killed.
Lemot Sediam Juste was a successful theater actor in his homeland, extremely popular and successful, but tended to be pigeonholed away from roles that called for greater dramatic depth. He wanted to be seen as a truly great actor, but whenever he starred in one of these roles, his efforts came across as melodrama or even comedy. He turned to writing his own plays, striving for the dramatic and gripping but achieving only the needlessly violent, using up his reputation's goodwill and finally turning the public on his efforts. He burnt down his theater with a full audience, his troupe, and himself still inside. He and his theater were resurrected, and he found that whatever he wrote on a script magically came to life on stage, but no matter how hard he tries, his illusionary characters ring false and his sets appear like matte paintings when lingered upon.
There was also Ravenloft's version of Bluebeard, who was married several times, kept demanding complete, utter and unquestioning loyalty from his wives, and when they inevitably failed, brutally murdered them. Now as a Darklord he keeps falling in love, again and again... but every time he does so, he sees his new lady love as one of his dead wives. Rotting flesh, dripping maggots, and all.
Malus Sceleris was the son of a powerful druid. His mother died when he was young and his father was often away battling threats, leaving him alone feeling that his father valued plants and trees more than he did him. One day his father came home wounded and Malus finished the job while "caring" for him by giving him blankets and bandages tainted by disease, afterwards destroying the forest grove his father protected. The Dark Powers gave him immunity to diseases in all forms and the ability to spread disease to others by touch, but also gave him the permanent and unavoidable ability to communicate with plants, who understandably did not have many nice things to say. In his domain, he has made pollution and corruption a way of life in a way a Captain Planet villain could only dream of, because if even a single blade of grass existed within a mile of where he stood, he would be tormented by accusations and guilt.
Meredoth was a powerful wizard and scholar from another world who wanted nothing more than to be left alone to pursue his studies in peace. In time, the ruler of his land granted him a distant landholding as recognition for his achievements and to get him out of the way. Meredoth was okay with this and saw the thinly-veiled exile as an opportunity for privacy and to get away from his obligations in the capitol. That is, until he found out his new land came complete with peasants who expected him to help them settle the new frontier colony. Eventually he got fed up with their complaints and needs and poisoned the entire population, transforming them into a unique form of zombie that kept their intelligence but did not need to be fed or sheltered. Thus freed of the hassle of human interaction, Meredoth continued his work until the Dark Powers swept him away. The Dark Powers gave him an uninhabited domain of his own, but also gave him the ability to spontaneously cast spells like a sorcerer, which to Meredoth is an insult to his long study and learning to have to use a "shortcut". The Dark Powers also took away his creativity so that he could no longer study and create in solitude; to get new ideas and explore new avenues of research, he would have to interact with others, which he cannot stand.
Abd-al-Mamat was in life a wise adviser to a powerful sheik. All in the kingdom recognized him as wiser and better suited to rule than the sheik, but he did not have noble blood. More and more often, the sheik ignored al-Mamat's advice and the kingdom fell into ruin until al-Mamat arranged his murder and "reluctantly" took power for himself, ruling with an iron fist but bringing prosperity to the kingdom and its people. He was corrupted by power and eventually ordered the execution of a man married to a woman whom al-Mamat coveted and took for himself. He was cursed and a whirlwind of swords dashed him to pieces. He lived on as a spirit and is immortal in almost every way, but he could not interact with the world or be seen as was forced to watch his kingdom fall back into ruins until the whirlwind of blades drops the last remaining bits of his body and he returns to life. Every century, he returns to life for one year and rules again, rebuilding his kingdom from a century of neglect and misrule, but at the end of the year the swords return and he has to watch again as his kingdom collapses without him.
The really twisted element common to all of these punishments is that the darklords' own character flaws which led them to commit their Acts of Ultimate Darkness in the first place are what truly make their existence in Ravenloft a living hell. If they ever worked up the moral strength to acknowledge their mistakes, Ravenloft would no longer be a prison for them. Then again, if they were capable of doing that they probably would never have become darklords in the first place.
More generally, if you're a D&D drow and Lolth gets annoyed at you, she's liable to turn you into a drider.
That particular example of the Punishment doesn't exist in 4e, for the curious. The games designers took a long look at the powers the drider gained (more innate spells, increased toughness, better combat ability), their similarity to the spider (a holy creature in drow society and by Lolth's religious tenets), and the fact that the drider form is generally based off of one of Lolth's own avatars, and asked themselves: "why is this supposed to be a punishment, again?" Being a drider is now a blessing, instead of a curse.
Originally, (1e), Lolth would test drow who got to 6th level. Those who passed were allowed to continue to rise in power. Those who failed got turned into driders - and their advancement frozen because of it. In other words, those drow who would be more useful at a higher level were allowed to get to high level, and those who weren't got Cursed with Awesome. Win Win for Lolth.
Especially because she believes in constantly testing the drow for hardiness and ruthlessness, the losers being eaten. Their transformation is a punishment for failure, but it's a spider because they've become an instrument for Lolth's will.
Magic: The Gathering has a few cards that feature this, mostly in black and red. Crovax comes to mind; for killing his guardian angel, he became the extremely powerful Phyrexian vampire overlord of an entire plane.
Every enemy in Silent Hill seems to be under some forced punishment from the town. Especially the second game. Monsters in straight jackets of their own flesh, monsters built into rusty cages... While these are mostly various characters' nightmares given physical form, the film version decided they were the actual townspeople twisted into monsters as part of Alessa's revenge.
Neverwinter Nights 2: Mask of the Betrayer: For the crime of betraying his god in an attempt to save his lover's soul from eternal torment, Akachi was turned into an immortal body-surfing soul-devouring manifestation of hunger by a particularly capricious god of death. This god may well have wanted to punish the country that created him, as he's never left it since becoming cursed. Of course, this was actually a Batman Gambit by said god to cheat death by ensuring that he wouldn't be forgotten, and thus his consciousness would be preserved; and the player has an option to punish the god in turn, in a truly ironic manner, by giving him a final death using the very "curse" he once unleashed.
Earlier, you encounter a plain, ordinary woodsman who was turned into a Shape of Fire, an epic incorporeal undead creature, as a punishment for guiding one of your predecessors (a spirit-eating psychopath) to where he could consume the spirit of Ashenwood.
The Big Bad of the Mega Man Zero series, Dr. Weil, had been placed in an immortal, indestructible human-reploid hybrid body, so he could suffer forever in his lonely banishment from Earth. Unfortunately, they neglected to make his new body incapable of, say, speaking and building things, so when he comes back, he resumes the world domination and genocide thing where he left off and is almost impossible to stop.
Apparently prior to certain changes necessitated to resolvePlot Holes, he was a teenage prodigy similar to Ciel (this is slightly more evident in the third game, where his speech pattern seems less like an old man's and more like a slightly immature teenager, particularly in his use of colloquialisms - can you see any evil doctor without an excuse referring to their nemesis as a "fun guy," non-threat or otherwise?). Considering that the suit also prevents him from aging, this would have just added another reason for Weil to go nuts and try to destroy everything, making this a case where turning someone into the Punishment is an excessivelybad idea.
Ignus in Planescape: Torment was a pyromaniac sorcerer who got brought down by the cooperation of basically every magic user in the Hive. They decided to punish him by turning his body into a portal to the elemental plane of fire, basically making him a Man on Fire on a permanent basis.
The only reason it worked at all was because it made him so happy that he just hovered there in contentment, even as a bar was built on the spot with him as the centerpiece.
The Nameless One himself could be seen as a self-inflicted form of the Punishment. He wanted to extend his life so as to have more time to atone for his crime, but messed up in that every time he cheats death someone else dies in his place and he loses his memories, keeping him from being able to fulfill his original intent and breaking the spell.
In Baldur's Gate 2, Jon Irenicus is under a terrible curse for past crimes. While the curse does NOT grant him any special ability, it did not remove the powers he already had... and Irenicus is an insanely high-level wizard. His attempts at removing his curse result in many deaths and a lot of suffering for the PC (and his/her sister). Unusually, the people at the origin of the curse actually see their utter lack of foresight come back to bite them in the butt.
Of course, that's because they're elves. If they weren't so long-lived, they probably would have escaped punishment.
In Shin Megami Tensei: Devil Survivor, Cain. For the sin of being the first murderer, God cursed him to be eternally reborn with a new body each time he dies, with all his previous memories intact. What does he do with this curse? Why, become an immortal chessmaster, of course, and spends eternity biding his time for the day he is able to take down God. In a subversion, it is revealed that God's intention was not to punish Cain but to give him eternal life so that he he would eventually come around to reflect on his mistake and try to atone for it: The 'punishment' aspect is more due to Cain's eternal bitterness and inability to see that he has the hope of atonement than anything else.
Raziel from Legacy of Kain was cast into the abyss, and after an eternity-long Painful Transformation he came back as a Noble Demon. In his first game he was also bound to the Elder God who (allegedly) resurrected him, and thus could not die.
The case with the famous Illidan Stormrage of the Warcraft franchise. Leaving out the debate on whether or not his punishment was just, Malfurion Stormrage and Tyrande Whisperwind took a powerful sorcerer and sentenced him to spend the rest of his immortal life chained up beneath the earth. Then, ten thousand years later, they are so desperate for a way to fight back against The Legions of Hell that they release him, only to find out that ten millennia of isolation have driven Illidan more than a little mad, making him even more dangerous than he was when he was imprisoned.
Warwick in League of Legends was cursed for his evil alchemy by getting turned into a werewolf. He rather likes his new form.
The Sins in Jack, due to their actions in life, are cursed with powers that seem awesome, but come with conditions attached due to the webcomic's heavy use of Ironic Hell.
In one episode of Tales from the Crypt Keeper an evil knight and his heroic squire set out to kill a vampire. After the knight abandons the squire to save the day alone he gets his comeuppance by being transformed into a vampire himself. This is clearly shown as a terrible punishment, ignoring the implications of a vain, cruel, greedy man being given powerful mind control abilities and Nigh-Invulnerability.