Evil Mentor



"Peter Petrelli: Do you know me? Adam Monroe: Of course I know you. It's me, Adam. Don't you remember? You and I are going to change history."

- Heroes, "Out of Time"

The Hero, or a member of the heroic band, finds a Mentor with new secret techniques to teach. The student eagerly signs on, only to learn later that there's a catch—the mentor is evil, has a hidden agenda of his or her own, and those new abilities are seriously nasty (though certainly not useless). The student may feel "soiled" by having learned these techniques and might swear off ever using them again, or they might have to wrestle with temptation against using them regularly. Of course, the audience fully expects that there will come a time of great need, and out will come the evil technique because It's the Only Way.

The Evil Mentor might teach the character Black Magic, a Dangerous Forbidden Technique, how to use a Deadly Upgrade (while downplaying the costs), advanced Psychic Powers like Mind Rape or Mind Control, and generally introduce them to abilities or substances that are painfully addictive and make Psycho Serum seem safe to use by comparison.

The Evil Mentor's motivation for this are similar to those of an Old Master, but with a Zen Survivor's more elitist air: they're looking for someone to carry on their legacy, warts and all, and usually against the pupil's wishes because only they are "worthy enough" to learn it. This usually entails actively corrupting the hero, not just to spread evil and deny good a powerful champion, but also netting him a personal Dragon. The Evil Mentor is also patient enough to wait, hoping that if attempts to actively corrupt fail at forcing a Face Heel Turn, then more passive temptation will do their work for them. Also, people who easily Face Heel Turn also easily Heel Face Turn. If you want quality in your minion, do it the long way.

For some Evil Mentors, it's a game of wits to see if their student's philosophy can stand against their own. After all, just beating someone in a flat out fight doesn't necessarily mean that someone is right. A slow battle for a soul can be just as rewarding; and honestly, more entertaining if the student's mind and heart is a Worthy Opponent. A gracious Evil Mentor will give their brand of help just out of curiosity to see how long Heroic Willpower can last.

A variant is the Evil Mentor's Book, which is not evil per se, but contains dark-side-y formulas and things the student might not be ready to learn. Unless, y'know, it's an Artifact of Doom, in which case it's an Evil Mentor in book form.

Contrast Deceptive Disciple, who turns "good" or honorable martial arts or powers on their head to achieve evil ends or inverts them into Black Magic. See also Bastard Understudy for a villain's voluntary apprentice.

If the mentor pretends to be a good mentor but is actually a villain out to exploit his student, he's a Treacherous Advisor. The step-down of this trope is the Broken Pedestal, who trains the student well, but is eventually revealed to be bad or corrupt much to the student's chagrin. See also The Svengali, whose purpose is typically to exploit the mentee for his own gain (and possibly the kick of exerting More Than Mind Control), rather than to pass on a legacy of evil. The Corrupter will often take on the guise of the Evil Mentor, though he doesn't have to; almost all Evil Mentors are Corruptors, but not all Corruptors are Evil Mentors.

Anime and Manga

 * Majin Tantei Nougami Neuro has Yako learning about the mysteries of humanity from a demon from hell, a sociopath killer, and The Yakuza. By the end of the manga, she takes all that she's learned from monsters and
 * Gundam
 * Paptimus Scirocco of Zeta Gundam ends up serving as a mentor for several other characters. Naturally, his harem of newtype pilots comes to mind most easily, but Scirocco also mentors Jerid Mesa and Yazan Gable throughout the course of the series.
 * Ali Al-Saachez from Mobile Suit Gundam 00 served as a Complete Monster mentor to Kurdish Child Soldiers, going as far as to instruct them to become Self Made Orphans in the name of "god". One of those children, Soran Ibrahim, eventually became Setsuna F. Seiei, The Hero of the series.
 * Master Asia of G Gundam trained Domon since childhood (before he became evil, though), and is revealed to be the Big Bad. He remains so for a good part of the show.
 * The Big Bad of Basilisk,, takes a boy in  and trains him as his apprentice and right hand, years before the events of the series start.
 * History's Strongest Disciple Kenichi introduces a whole organization of these in the manga after the arc covered in the anime called Yami. Unlike Kenichi's masters, Yami stresses the value of martial arts as killing methods. One member in particular  has taken an interest in Kenichi...
 * Mahou Sensei Negima plays a lot with this one, with Negi becoming apprentice to Evangeline, who holds a reputation as the most powerful, evil, undead vampire mage alive. Negi is fully aware of this, but trains with her anyway after deciding that she's not really that evil. And he seems to be right, regardless of how evil she claims to be.
 * Her case for villainy is definitely not helped by the fact that, aside from one or two Hannibal Lectures and an attempted seduction, her most evil deeds have been being a Clingy Jealous Girl and Sink or Swim Mentor-ness.
 * The Book of Eibon's Index/tables of contents in Soul Eater. Well, there is the whole . The fact that Negi isn't that bothered by it actually happening and is rather cheerful about it says something about Evangeline's effectiveness..
 * Code Geass R2 has Schneizel El Britannia playing this role, towards
 * Makoto Shishio from Rurouni Kenshin, towards Soujirou Seta. And even then, he was kinder towards Soujirou than his abusive stepsiblings ever were to him.
 * Dr. Umatarō Tenma from Astro Boy.
 * Orochimaru from Naruto seems to collect apprentices, and most of them wind up either evil and/or slavishly devoted to him.
 * Madara picked Sasuke up a while after he split from Orochimaru and did an even better job at this. The contrast between emo boy and the blank-faced teen who stabbed Naruto on his first appearance after the time skip was impressive, but the contrast between the shinobi who told his two minions 'no unnecessary killing' when they assaulted a whole fortress and the psycho who decided to off an entire village and threw away three loyal subordinates without blinking is also pretty wow.
 * Shimura Danzou did a version of this, too, though he tended more towards Svengali territory. With the More Than Mind Control conditioning and what he did to Uchiha Itachi and all.
 * The wolf becomes this to Chirin near the end of Chirin no Suzu.
 * In the original Yu-Gi-Oh!, Gozaburo Kaiba was this to Seto, at least in his own mind. While he was exceptionally harsh and strict to young Seto - and even abusive at times - he was trying to mold Seto into the ruthless tycoon that he was, devoid of emotion and able to continue his military firm. Ironically, this was Gozaburo's undoing. He specifically told Seto that to succeed, he could not trust anyone, not even him, and while Seto grew to despise Gozaburo, that was a lesson he learned only too well, using it to take over KaibaCorp in a hostile takeover and once in charge, proceed to destroy his adoptive father's life's work.
 * Yu-Gi-Oh! GX,
 * , aka Amnael to Judai, more so in the original version. Maybe more Well-Intentioned Extremist Anti-Villain than evil, but still fits.
 * Monkey Saruyama (called Mr. Shroud in the dub) was this to Ryu; a seedy duelist manager, he used brutal Fight Clubbing to help get Ryu back on his feet and back to the top of the Pro Leagues, but in the process, fully transformed Ryu from the honorable duelist he was to "Hell Kaiser", the selfish one who would win at all costs, no matter who he hurt. Unfortunately for Saruyama, it worked only too well; once Ryu decided he didn't need him, he fired Saruyama and threw him out of his car like garbage.
 * Divine from Yu-Gi-Oh! 5D's. As leader of the Arcadia Movement, he told his students (such as Aki) that he was trying to help them control their Psychic Powers. Truthfully, he was purposely making them even more destructive, hoping to mold them into an army of psychic assassins.
 * Sora becomes this to Zuzu in Yu-Gi-Oh! ARC-V, although at the time, Sora is still hiding his true nature.
 * During the Time Skip of One Piece, Zoro learned both sword mastery and Haki from the notorious Warlord Dracule Mihawk, in what was truly Training From Hell. Mihawk has stated that the two of them will be on opposite sides someday, and hopes that when this happens, no matter who wins, it will be the greatest battle of both their lives.

Comic Books

 * In Wee Tian Beng's The Celestial Zone, Xue Wu runs across one of these near the end of the series. Given that his insane competitiveness has been pushing him down the slippery slope, and that a villain recently gave him the If You Kill Me You Will Be Just Like Me speech right before he kebabed her, it doesn't end well.
 * Slade of the DCU does this as a hobby. He once acted as an Evil Mentor to Terra, before he realized too late that she was even more evil than him. He also tried to turn Nightwing evil in the "Renegade" storyline, but Nightwing turned that around by acting as a Good Mentor to Slade's daughter Rose which led to her Heel Face Turn. He also founded an Evil Counterpart to the Teen Titans twice. Slade in general has a disturbing interest in corrupting the next generation of superbeings.
 * Prometheus, also of the DCU, gives this a brief shot when he takes in a young sociopath named Chad Graham. He intends Chad to be his Robin, but the kid turns out to be a huge disappointment. Eventually he sets him on fire for his trouble.
 * Talon of the Fraternity of Raptors plays with this trope a bit. In War of Kings, he tells Starhawk the origin of his powers, omitting that the powers are actually for intergalactic espionage and assassination.
 * The Scarecrow has tried this a couple of times, encouraging young victims of bullying toward bloody revenge. He's had various degrees of success—one of his "students" prevented him from stabbing Batman, but kept and used a can of his fear gas.
 * The Heart of Hush storyline revealed that twenty years ago Scarecrow played this to a young Tommy Elliot - better known as Hush.
 * The Taskmaster is a Marvel villain who does this professionally. Occasionally working for The Red Skull, he hires himself out to train mercenaries and super-villains; while some of his students have become successful super-villains - or even heroes, more or less - in their own right; examples include Crossbones and Cutthroat (also henchmen of the Skull), U.S. Agent, Hauptmann Deutschland, Diamondback, Spymaster, the original Spider-Woman, and Agent X. Most of the time, however, he just trains thugs to be low-rent henchmen and cannon fodder. When working for the Red Skull, he can often cross the line to Treacherous Advisor at times, in one case sending the more disappointing ones to be "sparring partners" for his boss, which was a death sentence. On his own, he's more by-the-book, in case one hiring other super-villains to form formal academies, like the time Anaconda worked for him as a calisthenics instructor.
 * For a long time, Hawkeye's mentor was a villain (usually) called The Swordsman; note the similar costume design. Jacques Duquesne was a fellow circus performer and weapons-expert who taught young Clint Barton archery, but also tended to moonlight as a mercenary and assassin.
 * However, eventually someone at Marvel said, "Wait, wait, how can a swordsman teach a hero archery?" So via Retcon, they introduced Trick Shot as Hawkeye's actual Evil Mentor. Buck Chisholm was stated to be Duquensne's business partner and partner-in-crime, but in most respects, he's just a different version of the same character.
 * Spider-Man's enemy Dr. Octopus is this to both both Carolyn Trainer (aka Lady Octopus) and Angelina Brancale (aka Stunner, also his lover), two of the very small number of people to show Undying Loyalty to him. He was also this to Peter himself in the 1990s animated series.

Fairy Tales

 * In Farmer Weathersky, the boy's master teaches him magic but will keep him forever unless his father can find and recognize him, which he manages only with difficulty. Father Weathersky then tries to get the boy back with trickery.
 * In The Thief and His Master, the father only has to pay if he can't recognize his son, but the master uses magic to prevent him. And when the father succeeds, he tries to reclaim the boy.

Fan Works

 * Daniel to Danny in the Danny Phantom fanfic Daniel Masters. Slightly played with in that Daniel believes in Black and Grey Morality. He teaches Danny about some abilities, but—because he actually respects Danny's character—won't teach him the more... deadly skills until Danny asks.
 * Voldemort to Harry in the Harry Potter fanfic An Aunt's Love. Well, Bleys did say that Voldemort had to give him something twice, because of Voldemort's taking of his parents and his blood. This could be the way it happens.
 * Subverted in Harry's Savior, when Voldemort is actually turned back to the light.
 * While we're on the subject,  in Harry Potter and the Methods of Rationality. Rather than try to kill Harry, he's instead trying to bring him around to his point of view.
 * Lama Nawang in Fair Vote.
 * Inner Demons: Queen!Twilight Sparkle is this to her closest minions, Trixie especially.
 * The Pony POV Series has Celestia's Fallen Alicorn brother Morning Star having taught Discord how to be an effective Manipulative Bastard. Though, naturally, Discord was already evil before he ever started learning from Morning Star.

Films

 * Gordon Gekko from Wall Street.
 * Obviously, Anakin Skywalker and Chancellor Palpatine of Star Wars: "I can teach you things you need to know in order to save Padme. Oh, and you'll have to kill a bunch of kids for me too, but never mind that now..."
 * This actually happens so often in the Extended Universe (to Ulic Qel-Droma, Luke Skywalker, Jacen Solo...), it's practically a trope of its own.
 * One Expanded Universe source says that Watto (the junk dealer from The Phantom Menace) learned how to scrounge for parts and technology by living with the Jawas. By the time of the movie, however, he despises the Jawas, and just knows they're always sneaking into his back lot to swipe his best merchandise.
 * The Karate Kid Part 3 had Mr. Silver, slowly training Daniel to become more and more vicious in his fighting tactics. This climaxes when Daniel punches another guy in the nose at a dance, which makes him realize what he has done.
 * Jade Fox in Crouching Tiger, Hidden Dragon.
 * Los Angeles Narcotics Detective Alonzo Harris from Training Day is THE poster boy of this trope.
 * Henri Ducard in Batman Begins.
 * Sebastian Shaw in X-Men: First Class.
 * John Milton in The Devil's Advocate. Curiously, he doesn't actively encourage Kevin to become an Amoral Attorney (while indirectly encouraging him by surrounding him with the perks of being one) because he wants Kevin to choose that path himself.
 * Pai Mei to the Bride in Kill Bill.
 * A common interpretation of Hannibal Lector is that, in at least his own mind, he is this to Clarice Starling.

Literature

 * Many stories involving Mephistopheles - such as, naturally, Faust - portray him as this. He oddly does not seem to be the type of demon who tempts good men into evil acts, preferring to act as a backer to those who have already passed the Moral Event Horizon.
 * Littlefinger from A Song of Ice and Fire ends up becoming this for . He has ... paternal feelings for her.
 * The Dresden Files:
 * Justin DuMorne, Harry's guardian and first teacher in magic. Later in the series, the fallen angel Lasciel attempts to become an Evil Mentor by teaching Harry how to power his spells with literal hellfire.
 * Also Lea, his faerie godmother who, while she never tries to corrupt Harry, is extremely dangerous and not overburdened with morals, beyond the usual faery sensibilities.
 * In Ghost Story
 * Teresa Edgerton's The Castle of the Silver Wheel: the dwarf Brangwengwen plays this straight with Gwenlliant - Brangwengwen, a partially trained, elderly witch, knows the castle well enough to get into the Princess Diaspad's old rooms and thus to her old spellbooks (which feature Black Magic), and offers instruction in witchcraft to Gwenlliant (who otherwise has no teacher, and few people to talk to).
 * In In the Midnight Hour by Patti O'Shea, Ryne's mentor Anise turns to the dark side. Ryne doesn't know for sure during her years-long training period with Anise that she's secretly evil, but eventually figures out that she must have been bad all along. (You'd think Anise's kinky bedroom antics would have been a clue.) As the person closest to her, Ryne is assigned to be the one who takes Anise down, and she's afraid that she may turn to the dark side as well.
 * Another Evil Mentor's Book is the annotated Potions textbook in Harry Potter and the Half Blood Prince: Harry has no idea what one of the spells written in the book does until he uses it on Draco Malfoy and severely injures him. However Malfoy was trying to cast an Unforgivable Curse on Harry at the time.
 * Falcone in the Warchild Series plays this role for Yuri. He attempts it with Jos and Cairo, too, but they don't jump at his call and both reject his teachings at once. Only Yuri follows Falcone's training and instruction without protest.
 * Joruus C'baoth in The Thrawn Trilogy calls Luke to him, and for a few days Luke follows him around trying to learn from him, but quickly comes to believe that C'baoth was insane and had possibly fallen to the Dark Side. C'baoth believes himself to be the ultimate authority, naturally above those who are not Jedi. This is cinched when Luke tries to leave with Mara Jade and they are attacked, and later when they find that he was working with Thrawn.
 * Interestingly played with in Outbound Flight, with Jorus C'baoth (the original) and his interest in the fourteen-year-old Anakin Skywalker. The original C'baoth had a superiority complex and beliefs much like his clone's, though slightly less obvious. Obi-Wan is uneasy about this. Anakin, in some of the most subtle this-kid-isn't-gonna-turn-out-right characterization in or out of the Expanded Universe, thinks that C'baoth is awesome. He solves things so quickly, and he doesn't take nonsense from anyone.
 * The Return of the Home Run Kid by Matt Christopher (sequel to The Kid Who Only Hit Homers) is essentially the G-rated version of this. The mentor is a former baseball player kicked out for betting against his own team, and he teaches the main character tricks like how to fake getting hit by a pitch. (It's not entirely clear how this is worse than cheating through magic in the previous book, but it's pretty clear that we're supposed to see this as a negative development.)
 * Sauron was this to Celebrimbor in the Second Age.
 * No, he just deceives him. He is an evil mentor however to the last king of Numenor.
 * Morgoth was this to Feanor in The Silmarillion, and was reasonably successful until he implied he wanted Feanor's treasure.
 * The Morgawr to The Ilse Witch in The Voyage of the Jerle Shannara.
 * Viv Ivins in the Left Behind prequel books serves this role to Marilena Carpathia when she seeks to be pregnant and ends up becoming the mother to the future Antichrist Nicolae Carpathia until she is killed off.
 * In the Knight and Rogue Series the man who's name is not Jack Bannister is a varient of this for Fisk. The skills he was teaching were along the lines of conning and burlary, so it wasn't as though Fisk didn't know he was a bad guy, he just turned out to be a much greater Jerkass than Fisk had first thought. His last lesson to Fisk is that life sucks, and when Fisk finally recovers from the schooling, Jack tries to reinforce the lesson by.

Live Action TV
"Mr. Morden: It's like knocking over an ant-hill. Every new generation gets stronger, the ant-hill gets redesigned, made better. A few get lost along the way, yes, and that's unfortunate. I don't think it was ever easy, but you can't let that get in the way of the dream."
 * Buffy the Vampire Slayer:
 * Professor Maggie Walsh epitomizes this trope.
 * Mayor Wilkins represents an Evil Mentor / Parental Substitute to Faith, the series' renegade Slayer. While not directly causing her Start of Darkness, he genuinely cares for Faith very deeply. Perversely, Wilkins is the closest thing to a father that Faith has.
 * Also Gwendolyn Post, Faith's treacherous Watcher. Faith really can't catch a break...
 * Angel has Holland Manners, a senior attorney at Wolfram & Hart who considers Lindsey MacDonald as his protégé. He's actually quite similar to Wilkins from Angel's parent show, though he leans more toward the Ambition Is Evil side of things.
 * Averted with Zhaan in Farscape. She had to learn both offensive Psychic Powers and become willing to use them to beat the episode's Big Bad, both painful since she was a Technical Pacifist. Her teacher at the time was more of a Zen Survivor than evil though, but his lessons led to her using her abilities more assertively in later seasons.
 * In Season 2 of Heroes, Big Bad Adam Monroe takes under his wing resident Idiot Hero Peter Petrelli, successfully manipulating him into furthering his plans to release an apocalyptic virus upon the Earth.
 * In the same season, Sylar acts as a mentor to Maya, teaching her how to control her power without the help of her brother. And in late Season 3, Sylar himself meets up with his father, a Retired Monster who used to be just like him and who convinces him that he needs to stop hunting "small game" and go after real power. This eventually inspires Sylar to.
 * Ruby of Supernatural, even if her intentions are good
 * Specifically, she spends a season being mysterious and helpful before Dean dies, and then provides the bereaved Sam with emotional support, and encourages him to develop his Psychic Powers, which are of demonic origin, in order to avenge Dean. Even though he'd promised Dean he wouldn't use them.
 * It's notable that even though he showed a lot of The Dark Side Will Make You Forget markers, he never got further than rather lukewarm Well-Intentioned Extremist...unless he actually exsanguinated that poor nurse, Cindy, I guess, but that was a once-off. He trespasses rather badly against his family, but almost all of it is either under siren venom or in the throes of withdrawal. Sam is actually a really good guy, but no one including Sam really believes that even a little for much of season five.
 * The Yellow-Eyed Demon, Azazel, fancied himself this and sort of managed it, in a ham-handed way, with the rest of his specials, but Sam has a personal grudge and Heroic Willpower and a big brother, so it never really worked.
 * Lucifer toyed with the role as well. These fucktards will not leave Sam alone. On the other hand, Soulless Sam in six didn't need Samuel's influence to be a cold sonuvabitch.
 * Alistair to Dean. Plays up the avuncular thing kind of the way Azazel used to. Thankfully no signs of Stockholm Syndrome, at least not that survived his resurrection.
 * Season six, a bit. Not that the latter isn't the more powerful, but the former leads him by the nose with the hope of knowledge he can use to end the war, and his partnership with the devil's replacement drags him down until the Moral Event Horizon makes a faint whooshing sound as it flies by. Somewhere around the time he started killing his friends so they couldn't stop him, maybe? And then he succeeds, and goes batshit insane.
 * On Burn Notice, we learn that Larry Sizemore, the man who trained Michael Westen in most of what he knows, eventually faked his own death and went freelance. He's now a Psycho for Hire who enjoys using poisons and knives way too much, and thinks Kill'Em All is a legitimate solution to just about any obstacle.
 * On The Wire, Chris and Snoop, Marlo Stanfield's top enforcers, tutor  in the ways of the game.
 * Similar to the Batman Begins example, the mentor of Smallville's version of Green Arrow is a cold-blooded murderer and looks down on Ollie for becoming a superhero. In Season 5, Brainiac begins as one for Clark.
 * It's revealed late in Babylon 5's third season that view themselves as essentially this. They spread chaos and war and corrupt people because they are Social Darwinists who want to encourage people towards their version of 'freedom' and help them evolve by cutting loose all fetters and encouraging and aiding those with ambition.

Newspaper Comics

 * Parodied in Dilbert when Wally mentors Asok—the presentation is comparable to serious examples of this trope, but the actual content is training in how to avoid having to work while still getting paid. Asok may or may not be becoming more like Wally, but if he is, it's a slow process.

Theatre

 * Roy Cohn to Joe Pitt in Angels in America. Despite being a hideously loathsome man, he has a genuine affection for Joe, and offers him much in the way of (what he thinks of as) advice, which later leads to problems when Joe refuses to believe his "questionable but good-at-heart" mentor could do the kind of horrible things Roy Cohn really did.

Video Games

 * Knights of the Old Republic II:
 * Kreia states fairly early that she used to be a Sith, and tries to impart upon the main character the lessons of self-reliance, how doing good rarely solves anything, manipulating others to do your bidding, and a whole lot of other lessons that run contrary to the Jedi code.
 * Certain elements of the story allow the player character to play this role for the Handmaiden, the Disciple, Bao-dur, Mira, and Atton if you try to turn them to the Dark Side.
 * Kingdom Hearts series:
 * Riku had this as a recurring problem. The power he learned from Maleficent and Ansem was too useful not to use, but gave him serious self-image issues.
 * Also seems to be true between Terra and Master Xehanort in Birth by Sleep.
 * Goutetsu in Street Fighter, who taught a form of martial arts that used murderous intent in every move. Two of his students were Gouken and Akuma; Gouken purged the murderous aspects of the martial art and went on to teach this form to his students Ryu and Ken, while Akuma used the form as it was intended. Akuma used it to kill Goutetsu (who died happy, knowing his legacy would carry on through his student) and later tried to pass it on to Ryu.
 * The manga adaptation of Street Fighter Alpha by Masahiko Nakahira deviated from this back-story by making Goutetsu the one who purged the Satsui no Hadou from the art itself.
 * Houzuki from Sharin no Kuni is not only an Evil Mentor, but also the Big Bad, and doesn't make any attempt to disguise what he is - his Establishing Character Moment is shooting one of the trainees under his tutelage for being late to an appointment and Kenichi, the protagonist and his protege for the last seven years, is under no illusions as to what sort of person he is.
 * The Baron in Amnesia the Dark Descent is revealed to be this  towards the very end - though if the player didn't suspect this long beforehand, they might be carrying the Idiot Ball.
 * A book in Oblivion talks about how Nocturnal's cowl was stolen. A young thief tries to steal from a master thief, who summarily catches her but lets her be his protege. Eventually they plan a heist to steal the cowl of Nocturnal. The young thief is to wait in a nearby tree, wait for Nocturnal to remove her cowl, then let the elder make a distraction. When the distraction never comes, the young thief attempts to steal the cowl without help. After she is caught, she looks over to realize that Nocturnal's cowl is gone. When asked who she is, she says, "I'm the distraction."
 * in Assassin's Creed.
 * Muttonhead in Popful Mail. Before he became a notorious criminal, he used to be the mentor of Tatto, one of the heroes.
 * The Ancestor in Darkest Dungeon is either this or a Treacherous Advisor, depending on what interpretation of the facts you believe.
 * In Monster Girl Quest, Alice isn't truly evil, but the fighting techniques she teaches Luka seem rather dark and brutal, like "Demon Decapitation", "Cursed Sword", and "Bloody Fissure Thunder Thrust". Plus she eventually gives him Angel Halo, which is clearly an Evil Weapon.

Webcomics

 * Miranda West in The Wotch may qualify for this, given that she's keeping some very big secret from protagonist Anne and that she's willing to totally destroy the lives of a few people in order to make sure nobody interferes.

Western Animation
"Raven: It's dark magic! You've been teaching me dark magic! Malchior: Is it dark, or is it simply misunderstood... like you?"
 * Malchior in Teen Titans:


 * Ironically she ends up beating him with the same dark magic he taught her.
 * Slade and Brother Blood, too, at various points. Heck, Blood does this for a living.
 * Avatar: The Last Airbender: Katara meets Hama, a waterbender from their South Pole tribe, who uses her waterbending to take control of other peoples' bodies by "bending" the water inside their blood, and uses this power on innocent people in the Fire Nation town where she lives in revenge for her tribe being imprisoned by the Fire Nation. Katara is horrified and refuses to learn, but in the end must resort to using it on the Evil Mentor in order to save Sokka and Aang. Before being sent away, Hama "congratulates" her for using it and laughs. Katara was understandably upset. Ironically she used it on a Fire Nation soldier whom she thought killed her mother, but she's likely angry at Hama for teaching her bloodbending in the first place.
 * Chase Young of Xiaolin Showdown repeatedly tries to recruit Omi as his apprentice.
 * Psycho for Hire Lockdown plays this for Prowl in one episode of Transformers Animated.
 * Code Lyoko: Franz Hopper's diary accidentally becomes an evil data disk for Jérémie when he tries a technique... that almost kills him.
 * During one episode of Kim Possible, Shego became the Evil Mentor for Señor Senior, Jr. It worked very well, he transformed from Minion with an F In Evil to Worthy Opponent, until he was defeated by a Deus Ex Machina, and his newly found evil skillz were never mentioned ever again.
 * This is exactly what Big Bad Vlad Masters wants to accomplish with Danny in Danny Phantom. He only mildly succeeds because Danny goes through a dark arc.
 * Marathon loves this one. Diana Lombard had an evil mentor in Martin Mystery, and a minor character became "Admiral Admirable" with the help of one in Totally Spies!!
 * In the finale season The Secret Saturdays, V.V. Argost offers to teach Zak how to control his  powers. Being Argost, he admits to Zak right at the start that he intends to kill him in the end and  . And Zak still accepts...
 * The Archmage was this to Demona on Gargoyles. Also, the Weird Sisters are this to Macbeth and Demona.
 * In Ed, Edd 'n' Eddy, Eddy acts as a downplated example to Jimmy, teaching him everything he knew about scams - enough for Jimmy to use against the Eds and one up them at least twice..
 * In Transformers Prime (and its prequel book, Transformers Exodus), Megatron was this to Optimus Prime back when they were Megatronus and Orion Pax.
 * In SpongeBob SquarePants the Trope is often lampooned, having Mr. Krabs act like this towards SpongeBob, treating the role of a fry cook as Serious Business. The episode "Pickles" is a good example.

Real Life

 * Gilles De'Rais was this to Joan of Arc. While Joan of Arc would go down in history as a Saint, Gilles (the man who trained her combat and military tactics) would go down in history as one of the worst serial killers of all time. Which is kind of ironic in a way.
 * Elvis Presley's manager "Colonel" Tom Parker is often regarded as this and The Svengali to Elvis.