Kenshiro of Fist of the North Star is the successor to the deadly martial art known as Hokuto Shinken, which relies on hitting pressure points to kill your enemies in very gruesome ways (usually by making their heads explode). Ken also happens to be one of the kindest people in the entire Crapsack World he inhabits, and uses the pressure point techniques of the art to heal as well as to kill.
In Neon Genesis Evangelion, it's made clear from the start that Ayanami Rei is not a normal human, but somehow directly connected to the creation of the giant nightmare horror fighting, giant organic superweapons. Her actual purpose is to more or less extinguish all life on Earth, and her superpowers (which are not really on full display until End of Evangelion) are the same as those wielded by the giant monsters that are hell-bent on doing the same. Regardless, she is identified as one of the good guys... until she actually does use her power. But she did it for love, and mostly because Shinji told her to, so it's all okay.
Fullmetal Alchemist for almost all of the series, Scar's ability is to destroy things. Though alchemists don't see his power of destruction as evil, but merely as incomplete, as it is (together with understanding and reconstruction) a part of every alchemical transformation.
Also, Scar is not a good person, given the whole "State Alchemists killed my people, so I'm going to go around killing state alchemists. Wait, that child is a state alchemist, who quite blatantly was not involved in the war against my people, and is trying to stop me only because I am indiscriminately killing all these SA's? OK, superdeathgrab time for him, then".
This is really just how he is in the first anime and early chapters. Later chapters and Brotherhood either reveal more depth, or have him go through a redemption of sorts. Possibly both.
Princess Mononoke: The protagonist's arm is infected with some kind of tentacle-y incarnation of hatred, which among other things, allows him to shoot arrows hard enough to decapitate people and bend swords with his bare hand. He hates fighting, and spends most of the movie trying to end the war between Iron Town and the forest.
Soul Eater, everyone, heroes and villains alike, is either a human who can turn into a weapon and powers up by eating souls or someone who wields them (hence the title). The main difference is their choice of diet; the good weapons feed on the souls of evil people, whereas the evil characters feed on the souls of anyone they wish.
Some of protagonists are even still called Demon Weapons by heritage.
Arachne appeared to create the Weapons simply to see what would happen, and they've turned out various ways - some using their powers for good, others allying with the Big Bads, others just out for themselves. No-where does Arachne explain what she wanted the original/s for, and if its manifestation is the Nakatsukasa Purpose Tsubaki is host to, it isn't even inherently 'Bad'.
This trope is basically Kid's whole argument to the Witch Council as to why the DWMA and witches coexisting is possible. They have immense destructive power and a natural compulsion to use it, but it can still be channeled toward positive ends:
Kid: All humans possess a destructive instinct in them to a greater or less extent. Yet there are many ways to exhibit this instinct... If one craves to demolish something, there are many places that need demolishing.
Warden Magellan is literally a Poison Man. He breathes poison, he sweats poison, he eats poison, etc. He is one of the most dangerous people in the world. What does he do with those powers? He guards the prison of Impel Down and prevents all of history's worst criminals from endangering the general public. On the other hand, he's also shown to be very apathetic about the fates of his charges and has on several occasions killed a number of them for such minor offenses as being too noisy. To say nothing of the massively inhumane state of the prison in general.
Those said noisy criminals he killed were imprisoned in level 6 where the worst of the worst criminals belong and they were already destinated to die.
Brook has what he initially believes to be the power to bring himself back from the dead once—an extra life, in other words. However, it turns out that he actually has the power of spirits and the underworld. He can control the chilling winds of Hell and bring them into the mortal realm; move around souls, such as extracting them from people (including himself); and instill pure fear in others. Not to mention that he is an animate skeleton. In spite of these frightening powers, he enjoys companionship very much, is easily emotionally moved by stories people tell him, and is into planking.
Similarly to Magellan above, Coco from Toriko uses poison as his main weapon, but he is one of the nicest, politest and kindest characters in the entire series.
Sai Akuto of Ichiban Ushiro no Daimaou. He's a Nice Guy who wants to become a Messianic Archetype and make the world a better place. Unfortunately, as the person destined to become the next Maou (Demon King), Sai is a Person of Mass Destruction whose powers are geared towards causing as much pain and property damage as possible. One example: In chapter 3 of the manga, the students practice infusing their mana into living things using flower seeds. Rice lover Kena grew a rice plant. Junko grew a Mandragora that looks like Sai (which she immediately chopped in half out of embarassment). Sai...grewthis.
In Durarara!! we have Anri Sonohara. She's the host of the Evil Weapon Saika, capable of turning everyone it wounds into part of its Hive Mind... And yet she is a firm believer in that anything people do for her should be paid back (even saving the one person she absolutely loathes from what looked like a horrible death because he had helped her that one time back then), and she's taking Celty's advice to try and use Saika's power for the best to heart.
In InuYasha, Miroku's right hand is cursed with a vacuum-like supernova black hole (dubbed "Wind Tunnel") that he can barely control (by "control" we mean he can aim in a very general sense, and keeps it sealed with prayer beads when not in use). It has the ability to make anything disappear. Unless he defeats the demon who cursed his ancestor, it will eventually swallow him. Being a Buddhist monk, Miroku uses it as a weapon to protect the innocent. He never uses it on humans.
In fact, in his original meeting with Inuyasha and Kagome, Miroku attacks Inuyasha and attempts to suck him into the Wind Tunnel. Inuyasha is saved because Kagome takes a leap of faith and Miroku has to quickly seal the Wind Tunnel before she's sucked in. This being AFTER Miroku runs to a safe distance from town in order to avoid innocent victims.
He goes mad with power pretty much the instant he accepts that the Death Note works. By the original appearance of "L", he's already so far gone that he'll kill people for just challenging his authority.
Played Straight with Gelus and Rem-Gods of Death who are very protective of the people that have gained their love and loyalty.
Saiga, the hero of Speed Grapher is the only non-villainous Euphoric, and like the rest of them, his powers are a manifestation of his deepest (generally sexual) desire, and in his case, involves making anything he takes a picture of explode. Besides starting as a fairly good guy, an important part of his characterization is how he hates his powers and just wants to be normal. Because he was a famous war photographer and would sometimes get a Raging Stiffie when taking a particularly good photo, he's horrified by the implication that deep down he wanted to kill his subjects, and besides that, hates the fact that his powers make him unable to take a normal picture of anything.
In Medaka Box, we have Munakata. In a world of people with strange powers, Munakata was born with an abnormal desire and ability to kill. He is, in fact, a serial killer who first killed at the age of 5, and he carried more hidden weapons than anyone else, ever. Just looking at someone makes him want to kill them. Except, as it turns out, he's never actually killed anyone. His serial killer status and creepy talk of killing lives (literally, "will these kill your life?") are purely to scare people away so he doesn't kill them—the serial killer charge is all fake. As he says, his killing desire is the real deal, and he wants more than anything to kill people, but restrains himself. "Because, if you kill a person, they will die."
Lelouch from Code Geass has the power of absolute Mind Control, which (according to the novelization) he finds loathsome because he hates taking peoples' free will away from them. This serves to explain why he never really uses it to its full potential by ordering people to become his slaves until he crosses his Despair Event Horizon, and resolves to achieve his goals whether he needs to sacrifice his morals or even his own life.
Even after crossing the line, he prefers to use commands that have the smallest possible impact on the recipient to get the result he needs. For example, instead of rendering Guilford his mindslave when he needs his loyalty for something, he hypnotizes him to temporarily see Lelouch as Cornelia at the opportune time.
Tsubaki in Fafner In The Azure. Festum. Capable of mindraping people. Could fight by generating black holes. Someone else in similar straits to her is a hate-driven madman that is the closest thing the story has to an individual villain. Instead she's among the nicest and most considerate people in the story.
In Naruto, Shino (and every other member of the Aburame clan) was made into a living hive for deadly insects at birth, but he's one of the good guys and a reasonably decent person (though other people do consider him weird).
Similarly, Shikamaru (and the rest of the Nara clan) has the ability to manipulate shadows and control other people's motions (eventually gaining the ability to stab and strangle people), and Ino (and the other Yamanakas) has the ability to fire her soul into others and possess them (with other techniques including mind reading and making your opponents attack each other). Neither of them (or their parents) are even remotely evil.
For that matter, the Jinchuuriki gain powerful abilities by being permanently bonded with Tailed Beasts, gigantic supernatural creatures that are largely viewed as incarnations of evil. Some go screaming off the deep end, either due to isolation or the Beasts being dicks, but others, such as the title character, use the power this grants them for benevolent purposes.
The Mangekyo Sharingan, which can only be awakened by the trauma of losing a loved one, is one of Kakashi's most valuable abilities, and was used by Shisui in an attempt to avert a devastating conflict. Itachi's use of it also falls into this when he's resurrected and stops pretending to be evil.
The Second Hokage in Naruto has created a Necromancy technique which needs Human Sacrifice and rips souls out the afterlife (though he does get a few What the Hell, Hero? comments from other characters for inventing such a technique, including from the 1st Hokage). The Third and Fourth Hokages know a technique to seal souls in the belly of a Shinigami. Everyone with the title of Hokage has put the lives of their villagers well above their own well-being.
Gennosuke of Basilisk is a kind and honorable man who wants nothing more than peace, but he has a particularly horrifying and violent power. His Deadly Gaze ability fills those he's looking at with intense fear and pain, causing them to kill themselves in incredibly gorny ways. Interestingly, this power is actually well-suited to his personality rather than contrasting with it. He's a Martial Pacifist and his power involves directing others' murderous impulses against them. So, his enemies destroy themselves in the same way they wished to harm him.
Kagerou has a toxic body and Kiss of Death, but the series mostly depicts this as a tragedy for her because it prevents from ever having the chance to be the with the man she loves, and she's depicted sympathetically rather than as an evil person.
His genderflipped version in Devilman Lady has the exact same problem.
Hikitsu from Fushigi Yuugi Genbu Kaiden. One of his powers is a sort of hypnosis by which a person sees their worst memory or their greatest fear. Because he recognizes its cruelty potential (and it alienates him as well), he hides the eye with this ability under an Eyepatch of Power.
The main character of Psyren is the typical Hero archetype. Why is he here? His power, "Melchsee's Door", can be described as a super-destructive ball of shadow that attacks and destroys anything it sees as dangerous.
Berserk provides a strange example with Guts and Casca's child. When we first see it post-timeskip, it appears to be on the evil side of things due to being corrupted by Femto's demon-rape However, it turns out to be very loyal to its parents and uses its demonic influence to shield its mother from a mass of monsters that were drawn to her brand.
A one-shot character in the manga Slayers Special was Winnie, a girl with necromantic abilities so innate she uses them reflexively. However, she is actually very shy and is at first even scared of her own creations, despite being unable to stop using her powers. She genuinely means no harm, though.
Arguably Vash the Stampede from Trigun. Not only does misfortune and mass property damage follow him like a magnet, but his arm turns into a giant gun that blows up cities and put a giant crater in the moon. However, he is one of the most likeable and peace-loving guys out there. He even claims to hate the sight of blood. He has only killed one person in the entire anime, that being Lagato Bluesummers in one of the last episodes. And even then, Legato was forcing Vash to hold the gun to his head while readying to kill Meryl.
Ichigo has an inner Hollow that empowers him. It takes him a long time to master the power, and he goes through a few terrible experiences along the way.
His inner Hollow is actually tied with his real Shinigami/Zanpakutou powers and the Old Man Zangetsu is actually the representation of his Quincy powers. The origin of his Quincy powers is Yhwach, the ancestor of all Quincy. Yes, even more than Sousuke Aizen.
Sado and his super-powered arms. When in the hollow world, he can feel his power whispering to him and it's not a nice feeling at all.
The Visoreds, like Ichigo, have inner hollows that they've learned over a long period of time to control and use for beneficial aims.
Riruka's fullbring is rooted in a hollow origin. She had to learn the hard way not to use her power for ill.
Much earlier, Hayate from Magical Girl Lyrical Nanoha A's has the power of a tome that is known for its destruction powers in the cause of the history. Hayate is so nice that she manages to seperates the tome's corrupted Automatic Defense Program, and uses her power for good.
The reformed Numbers from Magical Girl Lyrical Nanoha StrikerS were built for war and fighting mages. Now they are either part of the TSAB or the Saint Church (which is part of the TSAB as well).
Thoma Avenir is infected by the Eclipse, a virus which turns the infectees into murderous killing machines who are depended to kill other people to survive. Lily Strosek, Thoma's Reactor Plug, is able to suppress the virus, so Thoma can use his powers to fight for good.
In Darker Than Black, the Contractor Shihoko has the horrible power of melting people's organs from the inside and the equally horrible Renumeration of regaining morality briefly after using it, prompting crushing guilt. She's not a bad sort, and tries to avoid using her power whenever possible.
Faust VIII in Shaman King, a necromancer descended from the original Faust, at first seems to be an example of Bad Powers, Bad People: he initially shows up as a villain (and incidentally, one of the only characters able to decisively beat Yoh), but later pulls a Heel-Face Turn after Anna brings his wife back from the dead and ends up falling into this trope instead. Later in the series, he focuses on being a superb healer rather than a strong fighter.
Black Bullet has the "cursed children," lolis that are born with the Gastrea virus in their blood and can manipulate the virus to grant themselves superhuman powers. This is the same virus that causes people to turn into Eldritch Abominationsincluding the cursed children themselves in a much slower rate. Enju Aihara, one of the cursed children, happens to be one of the most kind-hearted characters in the series.
Terrence Ward, AKA "Trauma," from Avengers: The Initiative, is this trope personified. He has the power to physically change himself into anyone's deepest fear. This certainly makes him a formidable opponent in combat. But the most interesting use of this power is for therapeutic purposes. As an aspiring therapist, he could help troubled individuals to literally face their fears, or otherwise put their minds at ease with it. An example: Henry Gyrich is terrified of falling victim to Alzheimer's Disease. Trauma then changes into Gyrich's deceased father as he remembers him.
"It's not in you, son... You're clean. Such a good boy, sticking with me to the very end..."
Laurel Darkhaven of Rising Stars used her power to telekinetically manipulate small objects to kill people... but her final act was to use those powers to make soil fertile again.
So was the more popular Rogue, whose touch could put people in comas (usually temporary, but sometimes permanently). She started out as a villain, but threw herself on the X-Men's mercy when the psychic echoes of Ms. Marvel's personality threatened to drive her insane; after spending some time with the team, she soon developed into a hero in her own right.
During the Punisher's "Angelic" phase, he had a run-in with Wolverine where they tried to stop a special Morlock with the power to spread death around her, killing anyone around her without a healing factor. To stop her from reaching the surface and killing the whole of New York, Wolverine and Punisher tried to stop her and in the end the angels called her to heaven. The worst part was that she wasn't evil: she was sealed in a tube by her parents when she was a child due to her powers and just wanted to be free, seeing people trying to help her as devils and people trying to kill her as angels.
Leetah in ElfQuest always uses her healing powers for good, except in one scene in "Kings of the Broken Wheel", where Rayek pisses her off so badly she uses them to blast him with pain, just as she's seen Winnowill do. Probably not a good idea, since he happens to be flying her somewhere at the time. He drops her. She survives. An interesting and continuing thematic between Leetah and Winnowill is that the only difference between their healing abilities is how they choose to use them. The proper name for healing in the ElfQuest universe? Flesh-shaping.
Raven, from several of the Teen Titans comic incarnations, is the daughter of the demonic Trigon and intended to serve in destroying the world. Instead, she opposes him and fights for good with the other Titans.
Possibly applies to the DC character Mister Bones. He is a walking skeleton (his skin and organs are transparent) and he has a deadly "cyanide touch" that can kill almost anyone he comes in contact with. Needless to say, he began as a villain. However, he has since reformed and is now the director of the DEO, a government department that deals with superheroes. He may not be unambiguously heroic, but is typically on the side of the good guys, or at least not actively against them.
It doesn't help that his most famous victim, Skyman, was killed when Solomon Grundy forced Bones to touch him.
Phobos, God of Fear, Son of War, in the Marvel Universe is a Creepy Child with fear based powers. He's an unambiguously heroic character.
Though he did cause a panic when he broke into the White House during the Siege event at the end of Dark Reign. It turns out he just wanted to talk to the president about the cost of lives that putting Osborn in charge had caused (including the life of his father, Ares). Since the president was naturally evacuated, he left a note on the desk in the Oval office... written in what looks like blue crayon.
And that was after seeing Ares ripped in half on national television. Some people would call that restraint, for a god.
The US army chose Flash Thompson to become the Venom-symbiote's latest host, putting it to use in the service of his country. Eventually, he made the transition into a superhero (unlike Normie, Flash hasn't convinced the symbiote to change; he does his best to keep it in check through willpower and drug-induced sedation).
The scarab of the Blue Beetle is revealed to be an agent of the Reach, an ancient enemy of the Green Lanterns who created the scarab as part of a hive mind that controls the wearer. Fortunately, the Blue Beetle's scarab gets separated from the hive mind, manages to develop a sense of self thanks to the good heart of its wearer Jaime Reyes, and becomes a sentient being of good.
The king of Inhumans, Black Bolt, can level a city, cause distant dormant volcanoes to become active once more, shake entire continents apart and generate tremors on the far side of the planet with a whisper. In fact, if he hadn't undergone rigorous mental training to prevent himself from uttering even the smallest sound (even while asleep) entire planets could be lost with a mere utterance of noise. He's got a power that an evil Omnicidal Maniac dreams of.
BIONICLE's Matoro got necromancy as his mask power during the Mahri Nui arc as a test of character. He ended up pulling a Heroic Sacrifice and becoming thought of as the greatest hero his universe has ever known.
Ghost Rider, the Spirit of Vengeance, is a monstrous being empowered by the Devil whose exploits involve a whole lot of serial Mind Rape. He's one of Marvel's most iconic superheroes, thanks largely to a generous dose of Pay Evil unto Evil and to his altruistic actions towards anyone who isn'ton his hit list. That Mind Rape ability? It's useless against people who AREN'T evil. The pain inflicted is based on how many sins / crimes the target has committed. So it's basically divine punishment, in the sense that you can't hide what you did.
However he did use this on a clown who had been forced to pretend to be evil as he was working undercover.
Liz Sherman has the power to burn things with her mind. When she was young she accidentally killed a dozen people including her family. For a while, she believed her power was evil, but later she learns to control it.
The spinoff series B.P.R.D. has Dr. Johann Krauss, a ghostly German scientist with the power to communicate with the dead and possess inanimate objects. He uses his powers to fight evil.
Etrigan from the DC Universe is a former knight of the Round Table with a demon trapped inside him. He is pretty much a good guy, and one of Batman's friends.
Ratman from The Elementals is a wererat and started out as a criminal, mostly because his rat-like qualities and rattothropy made him unpopular. He quickly changed sides after he developed a crush on Becky, who he subsequently strove to protect.
In Common Grounds...you'd think a guy like the Acidic Jew would be a bad guy, right? Acid touch and all that? But no. He concentrates as hard as he can to keep his powers at bay, and is always there to help in the event of crisis; he saved dozens of lives after the Oklahoma City bombings.
Marvel Comics' Man-Thing is incredibly strong and nigh invulnerable. Also, if you know fear, his touch will cause you to burst into mystical flame and die. Suffice it to say, he's utterly terrifying to behold. He's a good guy who had his own long running series. (Technically, Man-Thing isn't really a hero. He's usually not even sapient. That said, only villains tend to be burned by the touch of Man-Thing. You would think that a victim who went from being assaulted by criminals to having a Humanoid Abomination show up would be the most terrified, and thus attract Man-Thing's attack instincts, but in practice, it's villains' fear of justice that draws him.)
Then there are guys like Random. Random has the charming ability to turn his arms into guns. He can generate dozens of barrels from one arm and just start blasting away. Sure, he comes from the Dark Age, but he is actually meant to be a Totally Radical, happy-go-lucky guy who shoots a lot of people every day. He was on the X-Men. You don't see him much these days, for a few reasons; one of them is that he has basically the same power and personality as despicable villain Bushwhacker.
The (second) Scorpion, Carmilla Black, has a Touch of Death, but later learns that this power is both the only thing stopping her from being mind controlled by terrorist group A.I.M. and the only thing able to defeat their biological weapon.
Avengers Academy plays with this trope; The Avengers recruit and train several teenagers with either bad powers or budding sociopathy to specifically prevent them from turning into supervillains. How they eventually deal with this remains to be seen.
Mettle:"Look at us. Big monster guy, the human electric chair, poison gas girl, assassin chick, t-rex boy, and Chernobyl in Abercrombie and Fitch. One wrong move and any one of us could be a murderer."
Alpha Flight's Purple Girl/Persuasion had a rough start, but has consistently been one of the good guys since, despite the mind control powers she inherited from her evil father.
Nico Minoru from Runaways has a dark magic spell casting staff that emerges whenever she bleeds. She's also the kind hearted leader of the group who is noted to be too trusting.
Takato Matsuki from the Tamers Forever Series, is one of the nicest people you will ever meet. unfortunately, he is also the Vessel of Chaos and could potentially wreak untold havoc upon reality.
In Dungeon Keeper Ami, a heroic Magical Girl gets given all the powers (and landscape-corrupting effects) of Sauron. She proceeds, among other things, to devise a spell that eats evil-curses, figure out how to turn the ominous weather into electricity, and kill infections with a Necromancy spell.
The Powers Of Harmony: Libra and his Echo Blair are classic heroic knights, but in an act of desperation against Nightmare Moon's undying army, broke taboo and used Lifeforce magic, which turns the user into a nigh-uncontrollable addict who's as likely to kill his own comrades as his enemies.
Fluttershy is, as per canon, one of the nicest ponies you'll ever meet. However, the most powerful ability granted to her by the Element of Kindness is Fearsense, which forces the person on the receiving end to experience a vision of their worst fear, basically Mind Raping them.
The SI in With This Ring is a bearer of a Orange Lantern Ring, which utilizes the Orange Light of Avarice, and is powered by the users greed. It's only other user is an insane immortal that lives in cave, killing and devouring anything that enters, enslaving their souls in the process. He uses it to be a superhero, and fix the environment.
Luke Skywalker uses the Force choke on a pair of guards in Return of the Jedi, which Darth Vader does throughout the series. Luke just chokes them into unconsciousness rather than strangling them, though. Jedi all seem to have the same powers, with the difference being how and when they choose to use them.
In Revenge of the Sith, Palpatine argues that the Sith are all examples of this (or that they can choose to be) but that the Jedi refuse to believe it and tried to persecute them into extinction for exploring powers the Jedi considered "unnatural". The fact that he's a lying, manipulative psychopath responsible for a galactic war that caused billions of death to secure his rise to power casts doubt on his claim.
Expanded Universe materials, especially video games, have some Force powers, such as lightning, slated as explicitly belonging to The Dark Side, because they can only be used to harm. However, it's apparent that a sufficiently knowledgeable Jedi master understands these powers, even if they choose not to use them- when Dooku threw lightning at Yoda, the little guy just absorbed it.
Deadly Girl in The Specials can summon demons. She is a hero.
There's an interesting example in the most recent novels in the Discworld series. Sam Vimes is ... possibly the best word for it is infected ... by the Following Dark, a supernatural entity of vengeance. Vimes doesn't seem to have a lot of problems with it, because he already regarded himself as a monster with only his conscience keeping his darker impulses perpetually in check.
The Guarding Dark: Who watches the watchmen? Me.
In the Old Kingdom trilogy, the Abhorsens are a family of necromancers who use both Free Magic and Charter Magic to keep other necromancers in check. They can also walk in Death and use the bells like a necromancer, but they are always good people dedicated to undoing the harm done by necromancers and otherwise helping people. On the other hand, it is hinted that Chorr of the Mask was once the Abhorsen, but lost the correct respect for Death and fell first into necromancy proper and then into being one of the Greater Dead. So Abhorsen can go dark side, they just quickly stop being Abhorsen then.
The entire plot of A Fistful of Sky is Gypsum being gifted with the power of curses, which she has to use frequently or else, and how she figures out how to deal with this.
Cal Leandros uses his ability to create gates in the later books in the series in fights, to dispose of bad guys, etc. While the gate-opening ability in itself doesn't seem evil, frequent use of it leads to Evil Feels Good, with Cal on a raging high and feeling far less concerned about not killing his nearest and dearest.
Dorilys of ''Stormqueen!'' does manage to use her storm-control powers for good on a few occasions... but also kills people with them.
Merry Gentry: The Unseelie have always had pretty bad press, what with powers like turning people inside out, consuming them with magical green fire, stealing their virility, opening every wound they've ever had, calling all the blood from their body... They are the protagonists of the series.
From the same author, Anita Blake has the ability to turn a human into a living mummy fully aware of what is going on around him or her and in terrible pain. She uses this ability, or the threat of it, to get information used to save the day.
In the third book of Midnighters, we get to see the consequences of one character's temporarily becoming a half-darkling in the second book. Among other things, he can look at anyone and know exactly what they're afraid of, and to a certain degree imitate that fear (e.g. move in a manner reminiscent of a snake.) He loses a bit of his humanity, and pretty much becomes the Token Evil Teammate, but he's still a member of the group.
The Shining Ones from David Eddings' The Tamuli are an entire race of these. They're a simple, pastoral people, gentle to the point of pacifism. They also possess a Touch of Death that causes the victim to instantly and painfully rot away into a puddle of foul-smelling goo. The reasons behind it are quite complex, but the results are fairly simple - actually using their powers, even if it's absolutely necessary, causes most of them to burst into tears, or fall into a deep depression.
Some who cannot bear to kill are allowed to use use their powers to destroy the walls of a city, allowing the populace to flee for their lives.
Thanks to Lasciel, Harry Dresden had access to Hellfire, which is Exactly What It Says on the Tin. He continues to use it to do what he can to help other people. Though it's pointed out that it's affecting his subconscious - this motives don't change, but he gets more extreme and angrier. However, once Lasciel was no longer a factor, Harry lost this ability and was given the angelic equivalent, Soulfire, instead.
Then there's Thomas Raith, life-suckingWhite Court prettyboy ... who, instead of draining his victims dead, 'sips' from the customers at a hair saloon and fights on the side of the good guys. While Thomas Raith is still allied with Harry Dresden, his torment at the hands of a skinwalker makes him forsake the Friendly Neighbourhood Vampire status.
It's an ongoing question whether a person who uses Black Magic is redeemable. The fact that the White Council has a means for probational rehabilitation at all implies that it is, but we haven't seen it so far. Everyone who actually broke the laws of magic except in self-defense has slipped back into Black Magic regularly. Harry is more and more coming to suspect that this trope is totally averted for the Dresdenverse.
The Necromancer Kumori believes that she is this, but comes off more as a Well-Intentioned Extremist. Nevertheless, she did use necromancy to save a life; the guy was in total agony until the paramedics had him stabilised, but if he made a full recovery it might be considered worth it.
Harry Keogh, the Necroscope, uses his necromantic powers for good throughout the series; those actually called necromancers, however, not so much.
In Dragaera, Morganti weapons are evil weapons which devour the souls of their victims and seem to hunger to kill. Great Weapons are the same, but are much more powerful and even more sentient, and make the wielder feel good/protect the wielder. However, everyone in the series who has one- Sethra, Morrolan, Aliera, Telnan, Vlad is on the side of good (within the series' Black and Grey Morality). In the case of Vlad, the weapon itself qualifies, since it was created from the soul of one of the series' nicest characters.
Harry Potter speaks Parseltongue, the language of snakes. Most people think Parseltongue is an evil power, because several evil wizards (Voldemort being the most recent and bigger example, Salazar Slytherin the most famous) not only spoke it, but used it for nefarious purposes. Harry becomes ostracized for having this power, and only uses it for good, most notably to rescue his future Love InterestGinny Weasley. This becomes useful in Deathly Hallows, as Ron manages to imitate the word "Open", which he had heard twice (first when Harry opened the Chamber of Secrets back in book 2, and then when he opened the locket that Ron then destroyed). Harry loses this power after defeating Voldemort.
Then there are the "Unforgivable Curses": Imperius, Cruciatus, and Avada Kedavra, spells considered pure evil and worthy of life imprisonment. The spells are introduced in the fourth book, a good character uses one for the first time (maybe) in the fifth (Kingsley Shacklebolt might have used Imperius on Marietta Edgecombe, though it's also possible he used a Memory Charm instead), and by the end of the series Harry himself has used both Imperius and Cruciatus.
On the third hand, Cruciatus is shown to work only very poorly for anybody using it with half-decent intentions; it takes real malice to properly drive it.
Seth Sorenson from the Fablehaven series fights demons with his own dark-magic powers.
Melisandre of Asshai has among her magical abilities, the power to dispatch shadow-assassins to do away with her or her king's enemies. As to whether she is good, well, she maintains that she is, and she is fighting to save the world. Opinion on her is divided, however, but most readers would allow that she is at worst a Well-Intentioned Extremist or a Knight Templar.
Played straighter with Thoros of Myr, who is more or less a Good Shepherd and belongs to the same religion as Melisandre. His specialty is necromancy, which he seems to think is a Healing Hands type power. It may not be deliberate, but he functions quite well as a dark parody of the requisite cleric medic for an adventuring party. Even more hilarious is the fact that he joined the priesthood because he had nothing else to do, then woke up one morning to find his rituals did magic.
Valentine Ivashchenko's protagonist of Warrior and Mage and Dancing Flame, Vale, nicknamed "Black Earl", is a grand necromancer working by Dark Is Not Evil. He has kept his soul from the local Satan and in most cases takes power from things and ideas associated with secrecy, night and darkness, e.g. solitary contemplation, restful sleep or intimacy of lovers. Examples of good uses include:
Curing a plague released from a disturbed ancient burial site, although he used the responsible grave robber's forfeited life to fuel the spell. This was according to the Empire's law and with consent of the present heir to the throne.
Releasing the ghost of an ancient knight from a tomb by introducing said ghost to his direct descendant. The ghost is the founder of the Empire, the descendant is said heir to the throne.
Saving a dwarven tribe from an undead horde raised by making camp on a hill over another ancient burial site. In-universe quote: "Bringing together blood, fire and steel in any manner will cause nasty undead things to rise at most remarkable places."
Sealing the spellbook of the last grand necromancer inside himself to prevent power leaks.
Saving a girl from a voodoo-like curse. The girl is one of the Empire's princesses, and the curse part of an attempt to replace the Emperor, funded from outside.
Enchanting the steel layer of a ship's armour to prevent mussel growth.
Removing a curse from a trader's daughter.
Taking at least one Night Rider (a girl who has willingly sold her soul for revenge, e.g. after loosing her entire family and village, and works as a mercenary after completing the revenge) from death row, and later redeeming Night Riders in his employ.
Completing the local pantheon.
Saving numerous captives and Inquisition prisoners during the war.
However, the trope does not apply completely:
The losses in the war against the local Absolute XenophobeChurch Militant trigger a Roaring Rampage of Revenge during which Vale the Black Earl crosses the line. After finding those responsible for the destruction of his home castle and the death of all within including his parents, sister, pregnant wife and family-in-law the Black Earl began a dark ritual damning them one by one by Cold-Blooded Torture. His second-in-command struck him down, breaking the spell and making the death of the captives quick.
Given an aside mention in a short story in one of Bruce Coville's Book of Magic anthologies. In a world where most people get the power of wishing when they go through puberty, the main character's late aunt is mentioned to have gotten the power of curses instead. Since she didn't have anyone she disliked enough to curse, she didn't, and the unused curses built up inside and gave her cancer instead.
Jander Sunstar from Vampire of the Mists is basically good (although he does some very bad things) but at least some of his vampire powers, such as mind control, are at least morally questionable.
Like Rogue from X-Men, Juliette, the main character in Shatter Me has a fatal touch. She refuses to use it to harm people and hates being forced to use it for the bad guys aims, wanting to escape and live as normal live as she can.
Mr. Crowley of I Am Not a Serial Killer only wants to stay with his wife but he has to kill people and take their body parts to do it.
The heroine of Graceling has a supernatural gift for dealing out death. As she grows up her powers are exploited by her uncle, but at the start of the novel she has already managed to subvert this and turn her abilities to the good. During the story she develops her altruistic use of her power further, and develops a new understanding of it, that her Grace is not death but survival.
Mercedes Lackey's Children of the Night had a band member become a psivamp, someone who feeds off of the emotional energies of others and can affect emotional states to get the right intensity. This generally leads to either burning the victim out or giving him or her a fatal heart attack. As a psivamp weaned off of positive emotions and adjusted to fear and rage, he can't survive on food anymore. He eventually decides not to go along with his other psivamp bandmates and the vampire dad and has a fantasy of feeding only on the deserving, so he goes out and kills first a crackhead trying to kill him, then a pair of almost-rapists, before he realizes that the hunger doesn't distinguish between the bad guys and the victims, and he knows he'll slip. In the end, he helps take out the other psivamps, then commits suicide.
Averted with the Delphae in David Eddings' The Tamuli. They can read the minds of anyone they see (not their thoughts, the entire contents of the person's skull) and, with a touch, cause people to decay into puddles of organic goo. They are also quite pleasant people who stay secluded from the world because they can see how that sort of thing makes people nervous. They also hold as negative a view of their flesh-rotting power as others do, and one is left extremely distraught after being forced to use it to defend a friend's life.
The Zombie Master in the Xanth series can raise the dead as zombies, which curiously is portrayed as a positive power.
Well, that's because the zombies were generally nice people, if a little icky. Wait, not generally. ALL of them were nice people, that's it.
This is both subverted and played straight in Brian Lumley's Necroscope novels. In it, protagonist Harry Keogh learns as a child that he can speak to the dead telepathically. He eventually uses this ability to fight vampires and necromancers (and vampire necromancers).
The Necromancers are a particularly unpleasant bunch - especially the ones that learned to use their powers at an early age: this is because their abilities involve stealing the knowledge and strengths a dead body has gained during life, via dissection, dismemberment, cannibalism, and occasional necrophilia. Ouch. However, this is clearly meant to set up the Necromancer Boris Dragosani as a dark counterpart to Harry.
Averted in the Fingerprints series, where the psychics' powers have no relation to their alignment and some heroes have traditionally villainous powers like People Puppets. Note that this does not stop some characters from assumingBad Powers, Bad People is true, which is why Steve Mercer kills Amanda Reesce.
Averted in Perry Moore's Hero by Typhoid Larry, a sickly young man who can induce illness in others. Following the book's comedic tone, he's mostly played for laughs since his powers seem to have a greater affect on his teammates than the villains. Until the end, that is, when he really comes in handy. Sadly, we never learn much about him or his past, as he's the only member of the team Thom doesn't spend any one-on-one time with.
Graendal, in The Wheel of Time series, has an incredible talent for Mind Control—which, in the Age of Legends, she used as a psychotherapist. She eventually went bad (and began using her magic for more conventional purposes), but it had nothing to do with her powers.
In Orlando Furioso, Malagigi is a sorcerer who can summon demons but fights on the good guys' side.
Pretty much the point of Brimstone Angels. Heroine Farideh is a warlock in a Dungeons and Dragons setting, which means she gets her magic as part of a Deal with the Devil, and her powers are appropriately creepy and sinister as a result. That said, she's also a fundamentally goodhearted character who wants to use her abilities to do the right thing insofar as she is able; the resulting tension between Farideh and Lorcan (the devil aforementioned deal was made with) is a running theme.
Nico di Angelo in Percy Jackson and the Olympians. While hispowers aren't bad, exactly — just unsettling — they're definitely regarded as bad by many people, who believe Dark Is Evil. Nico himself is definitely good, if a bit damaged, and in fact pulls more Big Damn Heroes moments than almost any other character. His half-sister Hazel, meanwhile, is a much straighter example — one of her abilities is to attract jewels, but they're always cursed. She is still one of the most good-natured and helpful characters in the series, despite having undergone a Trauma Conga Line.
The novelisation of Development HellDoctor Who lost episode "Shada" runs into this due to Pragmatic Adaptation reasons - the original had an evil character, Salvayin, who possessed the unique and (in the setting) utterly dark ability to copy his own mind into other people's minds, but he did a Heel-Face Turn and became a good friend of the Doctor under another identity. Since this didn't make a lot of sense, the book establishes that Salvayin was never evil, and never even considered using his power for more than making people do silly dances at important political events and other such harmlessness - but the Time Lords assumed that he was evil, because if they had possessed his ability, they would have used it to take over the universe, and had no concept that he simply didn't want to.
Aiden and Grent in Rogue Sorcerer both use their blood magic for the forces of good, with Grent even sacrificing his own wellbeing in order to save Claron's life.
This is ostensibly the basis of "dirties" in Christopher E. Long's Hero Worship series. When you exhibit powers, you're tested, and only those with "clean" powers can use them to make money, while "dirties" are ostracized as being dangerous to be around even if they don't use their powers for profits. The actual reason lies in back-alley deals with unions to prevent superpowered individuals from taking jobs from non-powered workers. The clean/dirty line is based on quotas, not the actual nature of the powers.
Please Don't Tell My Parents I'm A Supervillain gives us Mourning Dove, an ostensibly heroic zombie construct of some type. There isn't much detail on her precise powers, but they're lethal and have created at least one vengeful ghost.
Live Action TV
Mostly played straight with Sam Winchester on Supernatural. His powers are demonic in nature, and he uses them to hunt demons. While he did manage to jump-start the Apocalypse, he was actually intending to stop it. But his addiction to demon-blood has led to some decisions that can charitably be described as "questionable".
He spent quite some time worried about "going dark side," and Dean's final wish at the end of season three was that Sam not use his demon powers. Knowing Dean would disapprove, Sam lied about it when Dean came back, and things got worse from there. It was never entirely clear how much of the problem was The Dark Side Will Make You Forget / This Is Your Brain on Evil, how much straight addict behavior from the blood, and how much Sam being an ass of his own free will due to trauma and pride. Still, he was trying to save the world and save people, even at his worst. And he gotbetter.
Clem, a demon, can manifest fangs, tentacles, and poison. The only times he seems willing to fight are when he sees a friend hurt, or to protect a threatened teenager. (He eats kittens, though.)
Angel and Spike are vampires, which in the Buffyverse is just an evil demon possessing a corpse, but manage to be good guys none the less. (Spike is especially impressive, since he pretty much made his Heel-Face Turn before he had a soul to induce it. Of course, both of them are still pretty big assholes. Angel sort of grows into his full assholishness as he gets a firmer sense of his own identity as a good guy on Angel.)
Anya, who is a demon as well. A vengeance demon - or at least she is for the start of her stay in the series. When she temporarily got her powers back, we see why this is a Bad Idea.
Ned on Pushing Daisies has necromancy powers, but attempts to use them as little as possible and generally only to solve murders, with a few glaring exceptions: his childhood girlfriend, former murder victim Chuck, his dog Digby, and Chuck's father Charles Charles, although he was not aware of his powers when he revived Digby. He remains the protagonist and a thoroughly good guy throughout the series.
Similiarly, Ted Sprague, who emits nuclear radiation. He learned to focus and control it after accidentally giving his wife cancer. When he gets arrested, despite being innocent, his first insistence is that he be contained in a radiation-proof cell so as not to pose a danger to his guards.
Bo, the main character, is the best example. Her succubus powers, which drain life energy from people she has sexual contact with, are so strong that she has killed people just from kissing them. Even so, she's one of the most unambiguously good people in the show, and has learned how to transfer life energy into people..
The Light Fae, who are gray in the show's Black and Gray Morality, have corpse-eaters and harpies as members. The corpse-eaters, called Aswang, are depicted as saintly old women, eating only the corpses without family and acting as a sort of supernatural sanitation service to keep diseased corpses from contaminating both the soil and the living.
Todd the Wraith from Stargate Atlantis might look VERY evil (plus, he can suck life out of other people to feed himself), but he's probably the only member of his race who doesn't backstab the team when he allies with them. Of course, he did it once, but only because he thought he had been double-crossed. As much as he likes to threaten everyone with feeding on them, he doesn't seem to actually enjoy doing it except when hungry. The only occasion when he did feed on Sheppard, he did so under duress. And even when Sheppard expired, Todd cleared the area first, fed on the attacking soldiers then revived him by giving back what he took.
To a lesser extent, Replicators. They may be universally evil, but when Weir became one herself, she didn't go wacko; instead, she attempted to make an organic body for her peers so that they can ascend. When that didn't work, she worked with her old team to set up a trap for the remaining Replicators, sacrificing herself in the process.
Niam. Despite being a Replicator, all he wanted was to learn ascension. Too bad he got reset by Oberoth into his default violent nature.
Plus the team themselves when they got copycat cloned by rogue Replicators, complete with rapid regeneration and everything. The part-human-part-Replicator clones even set up a distraction so that the real team can escape.
Huey: Hey, I never said I wouldn't use it for good!
Even though it's more like Bad Powers Chaotic Neutral people, you are perfectly capable of being a decent person in Mortasheen, even though pretty much every one of your Mons' superpowers will be Lovecraftian.
Dungeons & Dragons has a few ways of reflecting this character concept, particularly since 3rd edition.
In 3rd edition, only one spell from the Necromancy school is explicitly Evil: Animate Dead. If you can find a Lawful Good use for Circle of Death or Soul Bind, go right ahead.
The Malconvoker prestige class summons evil outsiders; one of the requirements is a non-evil alignment.
The supplement "Lords of Madness" includes the Fleshwarper class, which is based around turning yourself into a Humanoid (or not so humanoid) Abomination through grafts. The class's only alignment restriction is that you cannot be Lawful, so there can be as many good ones as evil.
The Warlock class in 3rd edition specifically must be either chaotic or evil to gain their powers. It's a safe bet that most Warlock players chose to be Chaotic Good.
And, due to an oversight, it's actually possible for a Warlock to be Lawful Good. Wizards of the Coast realized this late in 3rd Edition's lifespan and created a prestige class where the sample NPC is a Lawful Good Warlock.
The 4th edition Warlock is loosened up a bit - only some of their powers can be called "evil," and at the same time, there's no alignment restrictions, so it's not uncommon to find Lawful Good player Warlocks using hellish powers.
Thanks to there being no "evil" powers in 4th Edition, you can actually be a Good necromancer using the powers found in the book "Heroes of Shadow". Albeit, the powers are pretty brutal, but as long as you don't use them against anyone who's not evil...
The Lucifuge from Hunter: The Vigil are children of Satan who said "screw you dad" and now go around using their powers to fight monsters such as vampires and werewolves. Said powers include summoning demons, throwing Hellfire, making someone bleed out of their skin so that tracking them is easier, etc, etc. Not only do they use these powers to protect humanity, but they're actually one of the nicer conspiracies, in that they're actually willing to investigate the monsters beforehand in order to see if they merit destroying.
Unfortunately, there's explicitly a very good chance that having The Dark SideIn the Blood and using it eats away at any goodness you may have, given enough time.
In Vampire: The Masquerade you're a freaking vampire! Sure, powers like super strength, speed, and invisibility aren't necessarily evil sounding, but being able to rip the blood out of someone? Manipulate shadows? Control people's minds? Transform into horrible beasts and control bats and rats? Of course, it doesn't help that all powers are fueled by the blood of your prey. The good people part of this comes from how the standard vampire is someone following the "Path of Humanity" trying to keep themselves from giving in to the beast within, and hold onto human morals.
Exalted: Any heroic Abyssal or Infernal Exalt. Drawing power from the beings who created the Underworld with their passing and defined Hell with their imprisonment will do that to you. An Abyssal's powers are 90% about killing things, while Infernal powers are the actual abilities of their insane Primordial patrons. This makes heroism difficult for Infernals with the Ebon Dragon's charms, as he's pretty much the living embodiment of the concept of Villainy. That said, all is not lost. With a bit of reading between the lines, Infernals have Charms that help defend their loved ones, enable eternal unsleeping defence of your realm, create food, bestow useful mutations, cause injuries to regenerate, force corrupt gods to do their jobs, and rip the password to turn off the ticking soulbreaker orb right out of the bomber's mind. Even the Ebon Dragon's stuff can be used benevolently on the condition that one is being spiteful and malevolent towards worse people than yourself. Abyssals work on the same principle: no one said you could only kill decent people.
Averted in the tabletop game Mutants & Masterminds, where more evil powers are not restricted to evil guys, but just asking to be used. Who doesn't want the ability to sicken people by altering their nerve impulses with a touch (granted, it's the same power to sicken them any other way, but considering how many elemental themed superheroes there are, this is pretty much going to occur to everyone)?
GURPS Psionics rounds out its discussion of Psychic Vampirism by pointing out that one can use it to do things like leech away negative emotions (calming angry characters, soothing depressed ones, etc.) and remove debilitating nightmares—as well as attack villains, of course.
In Warhammer 40,000, having the ability to Mind Rape or kill in unbelievably horrible ways is generally grounds for immediate execution or corruption by Chaos, but conversely, it also makes one an attractive prospect for recruitment by the Inquisition.
Surprisingly, The Makuta were originally this. They were always beings of shadow, but the Brotherhood's original purpose was to create the wildlife of the world. In fact, the Brotherhood's original leader, Miserix, helped the Toa Hagah in their attempts to hunt down Teridax, the evil being most commonly known simply as Makuta.
Dark-types in Pokémon are called "Evil" in Japan and their attacks largely consist of inflicting pain or simply cheating. However, it's established canon that any Pokemon is only as bad (or good) as its trainer.
The lake trio in Pokémon Diamond and Pearl games are said to be able to steal people's memories, control their will, and remove their emotions, and, in fact, this is what the main villain was using them for — but they end up helping you save the world, and then go back home peacefully so you can catch them. Though, to be fair, those are really just outgrowths of their original abilities as the respective incarnations of Knowledge, Will, and Emotion used as defensive weapons.
Cynder, in her playable form from The Legend of Spyro: Dawn of the Dragon, after being exposed to Malefor's corruption in the first game, was given the powers of Fear, Poison, Shadow and, uh... Wind.
In Touhou, every character has a power, some of which are far more evil sounding or dangerous than others. For example, we have the curse-goddess Hina, who would normally use her cursing powers to spread misfortune and woe, but Hina's a nice person, who instead uses her powers to absorb misfortune and bring happiness to people. And after a brief bit of insanity, Utsuho is using her nuclear powers to run Gensokyo's first nuclear reactor.
Characters like Yuyuko have the ability to kill humans with nothing but a thought. What did she do with it? Heroic Sacrifice to save the world from a monster tree, turning her into a Cute Ghost Girl incapable of ever reincarnating (it's a gameworld based on Buddhism). Though she speaks casually of "inviting people to death", ZUN says that she takes her instant death power very seriously, and doesn't ever use without an extremely good reason.
Orin is a nekomata who collects corpses and lives with evil spirits that seek revenge. Don't let that fool you, she might play rough, but she's completely friendly and implied to have started living with Reimu as a pet cat.
Komachi, a not-so-grim reaper, ferries the dead across the Sanzu no Kawa (basically, the River Styx). Completely lazy, wants to do everything "at her pace", and makes for a great drinking buddy.
Yamame, monstrous spider with the power to spread diseases. Also a Cute Monster Girl whose only "spidery" appearance is in the clothing she wears. Word of God description: "Her power makes everyone she meets hate her. However, she herself wouldn't inflict disease on someone without reason. She's a bright, fun-loving youkai if you get to know her, so she's popular among the youkai that live underground."
In City of Heroes and its sister game, City of Villains, players can create heroes with skeletal wings, dark miasmic powers that suck the life from the enemy and hide allies in shadows, and the ability to nuke whatever's left until it glows.
The Going Rogue expansion allows characters to freely switch alignment. So you can have a demon summoning hero or an empathetic villain.
Canon character Infernal is a controller and binder of demons, who looks a lot like one himself. He's firmly with the good guys, though his Mirror Universe versionnote It's telling that Infernal is the only signature hero who has the same costume/name as their Praetorian counterpart shows us how easily his powers could corrupt him.
There are quite a few characters like this. Positron is basically a nuclear bomb in a tin can. Desdemona (Going Rogue's Poster Girl) is a reformed demon summoner. Sea Witch can summon the ghosts of the dead to do her bidding, yet spends most of her time fighting the evil Cage Consortium. Oh, and every Warshade ever.
In Guilty GearSlayer also fits. He's a very powerful vampire that sometimes drinks his wife's blood dry (infront of his foes) and the founder of the Assassin's Guild. But he used his powers only for good, even the guild originally before he retired was meant to put down evil people. After retirement (mostly in Accent Core story-line) he guides and advises other characters. Also his wife can't die so he can't suck her to death even if he wanted to. And he's a really nice guy all in all.
In World of Warcraft, there are Warlocks, who manipulate fel energy and command demons. Some are right bastards, but a number of them also fall under this trope.
There are also the Shadow Priests. The priest can go three ways: the Holy way of the healer, the Discipline way of the healer more focused on buffing, and the Shadow way of the damage-dealer is in a lot of ways even worse than warlockery. Shadow priest's signature techniques include utterly destroying an enemy's mind or controlling it, inflicting unbearable pain, consume an opponent's life and energy to revitalize the priest, channel the forces of Death itself, create beings made of concentrated shadow to serve the priest... As player characters, they can be as good as they wish.
As might be guessed by the name, Death Knights aren't using the most kind powers, but they can be played as rebels against their creator.
Nasus in League of Legends is actually a good person, but uses powers considered evil. For starters, he brings death, steal's people's life, gets stronger when he kills people with an attack, desecrating ground with spirit fire, and aging them to slow them down.
The Grey Order from League of Legends are Noxians who broke off from Noxus due to its evil, and study dark magic. Their representative Champion is Creepy Child Annie who is certainly sinister and uses dark magic to inflict fiery death upon her foes, but is, if not outright good, certainly not evil.
Kassadin has the powers of the Void, the same power coming from the Cute Monster Kog'maw that drove Malzahar evil. However, he only give into the Void powers to protect Valoran from the Void creatures.
A young nobleman you encounter in NieR fits this description. Going by the name of Emil, he's even-tempered and very gentle, but he also possesses a set of cursed eyes that instantly petrify anyone he looks at. He lives alone in a remote mansion with his faithful butler because he's afraid of accidentally petrifying anyone he gets near. Eventually, however, he finds a certain amount of joy in using his powers to aid your quest, stating directly that it's nice to be able to put them to good use for once.
Then, later on, he merges with his monstrous 'sister' and turns into a terrifying, floating Grim Reaper lookalike, with devastating magical powers, and a face that can turn strong men pale. And he's STILL one of the nicest people you're ever likely to meet. He might accidentally destroy a few villages when he loses control of his destructive might, but he'll feel REALLY bad about it afterwards.
In Yggdra Union and Blaze Union, we have Gulcasa and Emilia, who are both descendants of the demonic dragon Brongaa. Once their demon blood is unsealed, they're able to command insane amounts of power, if at the price of nearly-incapacitating strain on their bodies. Overusing Brongaa's power also threatens one's sanity if you happen to lose control of it. The main use of Brongaa's power, by the way, is in a technique aptly named "Genocide" that turns the user into an unstoppable berserker in exchange for the lives of his or her unit while bathing him or her in an aura of Hellfire. Gulcasa works hard to control his powers, and is using them to try to create a peaceful world where no one will have to suffer any longer. In the scenario where Emilia's blood is unsealed in Blaze Union, she's only fighting to protect her friends. Though it is possible for her to lose control, and the results are horrific.
Necromancer NPCs of Guild Wars tend to be either morally ambiguous, or have a somewhat skewed view of right and wrong. The Master of Whispers, however, is a genuinely heroic and wise old man in charge of a secret, ancient organization dedicated to watching for and battling forces of evil. The fact that he fights using plagues, curses, and the corpses of fallen enemies is irrelevant.
And of course, Necromancer is a valid PC class. There are no alignments, no Karma Meter and no moral choices, so the necromancers are just as heroic as all the other players (and in cutscenes, no one seems disturbed by the Bonehorrors, Bonefiends and Vampiric horrors that follow you around.)
The good-aligned Bhaalspawn in Baldur's Gate II, including good PCs and Imoen. Good people... whose divine heritage leaves them capable of transforming into unholy killing machines with a burning desire to slaughter everything nearby. Even when you can keep control of the slayer form, it still dings your Karma Meter.
Jowan from Dragon Age: Origins is also a blood mage, but while he does cause a few problems-most notably poisoning Arl Eamon-he also shows regret for his actions and expresses a desire to fix his mistakes. If sent into the Fade to fight the demon possessing Connor, he will never consider making a deal. Or if told to leave, he'll take on a new name for himself and help others escape the Blight. According to Word of God, Jowan was supposed to have been a companion to the Player Character, but was downgraded to just a NPC due to time shortage.
Most Mages in Thedas would argue this is the case, despite the Andrastian Chantry and Qunari's claims to the contrary. While there are always going to be a few who abuse magic, most want nothing more than to be allowed to practice their magic freely and live in peace. Just because they can throw fireballs at people, doesn't mean they will. Sometimes, the treatment of mages can cause them to become exactly what the others expect/fear of them. An escaped Qunari mage in Dragon Age: Redemption, when caught and asked why, explains that being told all his life that he was a dangerous, destructive thing and eventually decided to accept that truth.
The Grey Wardens are revealed to owe their success to this. During the Joining Ritual, they willing imbibe Darkspawn blood in order to take the Taint into themselves, granting them increased strength, stamina and complete immunity to the Blight spread by the Darkspawn. Sadly, this comes at the cost of only giving them thirty yearsleft to live, before they eventually succumb to it's effects.
In both Knights of the Old Republic games, a character CAN choose powers that go against his/her alignment, but the cost to force power will be greater. This goes both ways; healing powers cost more to a dark-sider.
Light-side Sith are perfectly viable in Star Wars: The Old Republic, and can be kind, honest, and honorable people whilst still utilizing the Dark Side and it's gifts of Force Lightning and rage-driven nastiness in combat.
Lord Praven is an example in the Jedi Knight storyline, he's an honest and honorable Blood Knight willing to give the player character an even chance of stopping his plot. It is possible to redeem him after beating him.
In Jedi Academy, Kyle specifically tells you that Force powers aren't inherently good or evil, it's how you use them that counts. For some reason, this doesn't keep Luke and him from berating you if you do decide to only use the "Dark" powers. That said, Kyle himself openly uses Force Lightning as a light-sider.
The Force Unleashed shows this in the form of Galen Marek/Starkiller. Granted, he starts out bad as Vader's secret apprentice, but as the game goes on, he finds himself fighting for the very side he was sent to destroy. Even so, he frequently uses Force Lightning every few seconds, and in the sequel, he gets the ability to max out his power by tapping into his fury, and using it to channel his attacks into unstoppable blasts.
The Shin Megami Tensei series has Mudo skills, which are based on darkness and can be used by both demons and humans.
Persona 3 has another example in one character who's closer to bad purpose good people. The entire reason for his existence is call Nyx to bring The Fall. However, due to gaining human form by means of a particular event ten years prior to the game, he is willing to at least try to delay The Fall even though he thinks that it is inevitable either way.
Malpercio from the Baten Kaitos games. Despite making a Deal with the Devil for dark powers, they're just normal people who are desperate to stop something far worse. By extension, Sagi could also qualify, seeing as how he gets his power from a chunk of Marno.
Donovan Baine in Darkstalkers is a Dhampyr, or half-vampire. As such he is a powerful foe owing to being a creature of the night, and is shown in the questionably-canon anime to be a very powerful and resilient character. However, he laments over his 'cursed blood', looks after an emotionless psychic orphan, appears to be a pious Buddhist monk and generally does what he can to help protect humans from the less benevolent Darkstalkers. All of this with a demon broadsword as tall as he is on his back. Hsien-Ko and Mei-Ling (Lei-Lei and Lin-Lin in Japan) are lesser examples.
While not evil in itself, the Satsui no Hadou from Street Fighter roughly translates as 'the surge of murderous intent'. The known practitioners are all good (Ryu and Ken), not true users (Sakura based her style off of Ryu's), have perfected it to the point where the desire to kill is suppressed (Gouken) or morally neutral (Akuma/Gouki, who is driven to be the best fighter in the world, and will not kill a weak opponent, but will not hesitate to utterly destroy a strong one).
In Kingdom Hearts, Riku ends up in this dilemma after being released from Ansem's control in the first game. He assumes Ansem's form and dark powers again after 358/2 Days's events in order to capture Roxas, knowing full well he may be screwing himself by doing so. Thankfully, it's resolved by the end of II.
Ashley in Wild ARMs 2 gains the power of the evil Lord Blazer very early in the game, and spends most of it determined that evil power can be used for good reasons.
Blue Mages (and various equivalents) in several Final Fantasy games can learn attacks & magics that are unique to enemies (pretty much Bad Powers by definition), but are the good guys.
The powers of the Dark Knights usually involve inflicting suffering, bear such ominous names as "Charon" and in at least one game were shown to have the ability to drive their users insane, but plenty of good guys in the series fall into this class.
This is discussed in The Reconstruction—the "Noxious" element is directly opposed to the "Holy" one, and it's generally perceived as purely destructive, so the PC who specializes in it tends to worry about whether it will corrupt him. He's one of the nicer folks around, though, and eventually, he decides that Dark Is Not Evil.
In Dungeons & Dragons Online, a player can build a mage character as a necromancer and slowly become a lich over time as they reach max level... and be Lawful Good all the way. In fact, it's impossible to be any moral alignment but good or neutral, though lawful and chaotic are still open.
In Suikoden the Soul Eater Rune - as its name suggests - consumes the souls of friends and foes alike, but both of its known wielders are good guys through and through. At the end of the first game, Windy attempts to take the Soul Eater from Tir by force, but it refuses to accept her as it's master, even though, as she said herself, she was its ideal host, reveling in death and destruction, just like the Soul Eater. The Night Rune allows the existence of night creatures like zombies, but it's also only been used by good guys to slay vampires and such. Finally, while the Moon Rune, with its ability to bestow vampirism, has been used for evil purposes, its original bearer used it to save people who traveled into her forest and allowed the vampires she created to thrive without the need of blood.
The Rune of Punishment burns through a lot of bearers and does have a few 'bad guys' for bearers...but it isn't picky, and overall, its bearers tend toward unfortunate bystanders with varying degrees of innocence before an Artifact of Doom fused itself to their hand.
Kerrigan in StarCraft II: Heart of the Swarm is a former Fallen Hero who was, in the previous games, one of the most reckless and vicious villains. After being partially turned back to normal at the end of the previous opus, she is now more of an sympathetic Anti-Hero who actually tries to be a better person. Her powers still consists in unleashing a Horde of Alien Locusts to slaughter her ennemies, though.
The Necromancers in the Diablo franchise are an order devoted to maintaining the Balance Between Good and Evil, but because Hell has the upper hand 90% of the time, in practice most of them are strictly heroic.
Shiki of Tsukihime. With his demon assassin abilities and Mystic Eyes of Death Perception that shows him, "To kill this person cut on line / stab at point here," the only reason he isn't the Grim Reaper incarnate to anyone within his knife's reach are the migraines his powers give him while sapping his life away. But he acts just like an Ordinary High-School Student.
Shiki of Kara no Kyoukai has much the same issue, only she does NOT have the headaches, and doesn't bother going to school. She's still neutral at worst.
Also in the Nasuverse one can make a credible arguement for Rider of the Fifth Grail War. Her real identity is Medusa and most of her Noble Phantasms aren't that nice. Blood Fort Andromeda drains people of their energy and eventually reduces them to piles of blood and organic ooze. Summoning her mount, Pegasus, involves creating a spray of blood by stabbing herself in the neck and the bridle Bellerephon is used to whip the normally docile beast (which in some interpretation of the myth is her own child) into insane fury and bloodlust. The only exception is her mask, Breaker Gorgon, which seals her mystic eyes. Rider herself however is actually quite a nice person and something of a Woobie once you get to know her.
The "Bad Boys Love" route of Hatoful Boyfriend indicates that this was true of Fujishiro Nageki when he was alive; he was the carrier for a fast-acting lethal-to-humans virus, and committed suicide to stop Dr. Shuu's attempts to weaponize it. By the end of the storyline (assuming you get the good ending), Ryouta becomes a carrier for the same virus and chooses to be isolated to prevent it from spreading, hoping only that he'll be able to be cured some day.
Aoba of DRAMAtical Murder has the ability to Mind Control and Mind Probe people with his voice, an ability that can permanently destroy people's minds if abused, and his powers are explicitly linked with death and destruction. He also has a Superpowered Evil Side that grows stronger the more often he uses his power. In spite of all of this, he's an unwaveringly good-hearted and selfless person who's horrified when he accidentally renders one of his friends comatose by entering his mind and finds a good use of his destructive powers in exorcizing the mental demons tormenting his friends/love interests.
The same could be said of Aoba's twin brother Sei, who has the ability to brainwash people by merely looking at them but turns out to just be a lonely and abused pawn of the Big Bad who asks Aoba to Mercy Kill him when they finally meet.
Rilian from Dominic Deegan seems to embody this - as the first Necromancer, he uses his powers to help maintain the balance between life and death. And mess with people's heads. And Kick Jacob Deegan in the head until he understands that Death Is Not Zombies.
Of course, when we find out that a few hundred years ago he was a jolly, friendly plump guy who seriously considered calling his new form of magic 'deathomancy,' it's a little sad how completely he's become what he is today. Dark may not be evil, but evidently it wears you down. Or maybe that's the thankless centuries of world-protecting with the face of a skull.
The strip plays Bad Powers, Bad People straight with all the infernomancers, though. They sold themselves to hell for power, and apparently it is either impossible to do that with good intentions, or impossible to hold on to good intentions for more than five minutes after doing so; "there is no such thing as an infernomancer with a heart of gold." Bulgak Adrak cannot escape Hell until he fully accepts that he earned his place there and repents. His soul then explodes. This is a good thing.
Word of God says the demons are all fully, fundamentally evil for the same reason. They can't become demons without actively participating in the evil that is hell. Karnak has still managed to become a mystery on this score without truly approaching Noble Demon, only partly because since the war in hell he has started to get all kinds of really kick-assmoments.
The mystery is resolved with The Reveal that Karnak isn't a true demon, but a human mutated by the powers of Hell. He's still not a good person — good people don't try to Murder the Hypotenuse or attack children — but he isn't fundamentally evil.
Zoophobia's Damian possesses immense demonic powers and shapeshifting abilities, but chooses to use them for nothing more than harmless pranks and to mess with others.
In an Order of the Stick Dragon Magazine comic, a Medusa informs Durkon that she doesn't want to hurt people, so Durkon sets her up with a job where she petrifies the terminally ill so they can be de-petrified when medical science advances enough to be able to cure them.
Later on in the story, Durkon is vampirized by Malack, but returns to the Order after the latter's death and states that at worst he's probably no more evil than Belkar.
Unfortunately, He lied. When vampirized, Durkon became the victim of a Grand Theft Me. Durkon's spirit was left helplessly trapped in his mind, where vampire-Durkon is free to look through his memories in order to fake being the real Durkon.
Ruby, with her third eye, qualifies here. The eye can see things that her normal eyes can't, which did come in useful on a couple of occasions, but it also hurt like a motherfucker and bled rather nastily each time she used it. When it started to feel good, the genre-savvy players wisely decided to avoid using it.
In Sluggy Freelance, Torg gains a magic sword that can kill just about anything. This isn't so bad, since "anything" includes murderous, soul-stealing demons. The catch is that, to use this power, the sword needs to feed on the blood of the innocent before battle. Fortunately or unfortunately, Torg is usually able to find plenty of innocent people bleeding to death when he really needs it.
Capricorn from Zodiac is demon-possessed and can willfully (and sometimes unwillfully) transform from introverted teen to fire-breathing monstrosity. She is not particularly fond of this situation and was quick to ask Aquarius to exorcise her when she found out that Aquarius was an advanced magic-user. Aquarius explained that she can't because demon-possession was of a different religious school.
In the webcomic "Zom Ben", the title character is a superhero whose power of turning into a zombie is gained from an amulet that Set gave him.
This is pretty much the entire premise of Zebra Girl. It starts off with a carefree, lighthearted guy playing around with a book called the Tome of Evil Said tome accidentally (maybe, turns out it's sentient) turns his room-mate into a demon-girl, whose unique stripes and hooves makes her the titular heroine of the strip. Now SHE'S the one with the bad powers, but it trying to keep as much of her life together as possible... While making things spontaneously combust when angered, having claws that can shred anything, every bodily fluid (Word of God says yes, every fluid) being highly corrosive, and gaining sustenance by devouring life force. And coffee, which somehow is the only thing she can still taste properly given the acid-saliva. It's one long struggle to enforce this trope instead of slipping into Evil Feels Good. Then, to defeat an enemy who has completely embraced demonic power, Shandra does as well... and doesn't look back, inverting this trope for a very, very long time in-universe.
Cody Giles, AKA "Odelarch" from Angel Of Death is, in his true form, a large, putrid walking corpse whose powers include devouring the soulsof the living and pooping them out a slaves he can use to spy for him or animate corpses, making any material (including dead flesh) rot at hyper-speed, killing anyone with a touch, inflicting any dissease on anyone with a touch, and draining all of the light out of an area around him. He wears a Black Cloak and wields a Sinister Scythe. Despite all of this, he is an incredibly moral character, who is constantly concerned with doing the right thing and only devours human souls because if he did not, he would soon starve himself into a frenzy and eat hundreds of people.
Other Liches, though, are much less benevolent.
Shadowcloak from the Global Guardians PBEM Universe. She can generate a "living darkness" that "feeds" on people's body heat. You just don't see too many heroic energy vampires.
Tennyo from the Whateley Universe is effectively a human machine built for destruction. She's also a very shy girl firmly on the good side who likes reading and ballroom dancing.
Sarah Waite aka Carmilla. Daughter of the demon Gothmog, granddaughter of the Shub-Niggurath, descended from Cthulhu on the other side of her family, has Lovecraftian Superpower, eats by sucking the lifeforce out of living creatures, and is predicted to wipe humanity off the face of the earth to be replaced with her spawn. She's one of the good guys.
In Whateley Universe (like Maggot and Killstench), Gotterdammerung can disintegrate matter by touching it, sometimes by accident, and his upper limit is somewhere around 700 kilograms. Carmilla is a multiple murderer who absorbs the life force of things by contact. She's trying to be a hero.
Worm features several examples, starting with the protagonist: Taylor's power is to control swarms of bugs. The Squick imagery of her power is probably a part of why she is mistaken for a villain on one major occasion, and if she is not careful, offensive use of her power carries the possibility of anaphylactic shock (bee stings), comas (black widow spiders), tissue necrosis (brown recluse spiders) or death (all of the above). Despite this, she has aspirations of being a superheroine and is constantly striving to do the right thing.
There's also Crucible, of the Brockton Bay Wards. His power? To make a solid force field bubble, which he then fills with an insane amount of heat, incinerating everything inside.
John Lant from Phaeton tried to be this but died before he had a chance to use them.
Zak Saturday from The Secret Saturdays. His cryptid controlling powers turn out to be the powers of Kur, the most evil cryptid to ever exist. Naturally, Zak fights against this dark nature within him and uses it to do good for the world. Although unlike some cases, he doesn't fully overcome the darkness within him as his powers are taken from him by Argost (who ends up destroying himself due to already having the antimatter version of that power), leaving Zak as a normal person.
In Avatar: The Last Airbender , firebending is an interesting example. At the time Avatar: The Last Airbender takes place, the Firebending style that most people know is fueled by rage and hate. But a few characters, like Jeong Jeong and Zuko, have been known to use this style without becoming really evil, and we are shown enough to see that even the storm-trooper-like firebending Faceless Mooks are just guys (and possibly girls) who happen to have taken the standard career path of 'benders in their nation and joined the army, which happens to be conquering the world. They presumably possess a standard variety of personal moralities, although the propaganda they're raised on can't help anything.
And the true, original style of Firebending, which Zuko later learns, is a creative, life-giving force (like the sun) taught to mankind by benevolent dragons. Aang and Iroh have also learned this style from the dragons.
Jeong-Jeong is a curious example in that he managed to turn firebending into something more defensive (though not entirely harmless) whilst still firmly believing that firebending was an inherently destructive ability, and envied the healing skill of waterbenders. Zuko, by contrast, needed to find the original source of firebending before turning his practice of it to a more positive use.
Not that his use of it to express his feelings by turning the campfire into a pillar of flame in the Beach Episode wasn't kind of cool, and basically harmless.
There's a firebender in the first season who uses his abilities to make fire dragon constructs to entertain the crowds.
Marceline from Adventure Time is a vampire, and can turn into a hideous monster when upset, but certainly isn't a bad person.
Flame Princess burns pretty much everything she touches, and has a compulsive need to destroy things, but is still a perfectly nice girl.
Danny Phantom's Ghostly Wail. Danny first learned of this power when he saw Dark Danny using it. Since its only use is for total destruction, and the fact that it severely drains him of energy, Danny only uses it as a last resort.
In The Venture Bros., Dr. Orpheus is a necromancer (though he says he uses the title because it sounds cool, he has done genuine necromancy) and is not only a good guy, but possibly the nicest character on the entire show.