Let me tell you my evil scheme I'm gonna enslave your minds with a predictable melody And uncomplicated rhymes And if I asked you to, you'd even change your name to "Amy" Because you're gonna yodel-odel-odel-obey me
There is this one pop singer, who recently became the biggest thing since television. She's beautiful and came out of nowhere all of the sudden. Oh, and her voice is so wonderful and clear and great and, and, and...Ah, let's just listen to her new single! ...Oh wait, how come I'm so tired suddenly? Why are the words "OBEY ME" stuck in my head? I don't remem...Oh, Crap.
Congratulations, you encountered the Evil Diva! With her magical voice, microphone, instrument, etc, the Evil Diva becomes a rising star and draws all of the world's attention to herself and her "talent". Her songs may seem better to you than they actually are, hypnotizing you, turning you into The Heartless, stealing your soul, or the like. She's also always female and usually a poster-child example of Evil Is Sexy. She's a subtrope of the Idol Singer and may or may not overlap with the Dark Magical Girl. As such, she has a tendency to pull a Heel-Face Turn.
The Hero may or may not be immune to the effects of her music. His/Her Sidekicks or True Companions are usually not. Her fighting style usually incorporates The Power of Rock, and her appearance usually signals a Musical Episode.
Compare Magic Idol Singer, of which this is the Evil Counterpart.
Not to be confused with the webcomic Evil Diva.
While not evil per se, Onpu Segawa from Ojamajo Doremi was an Idol Singer who used her magic for her own selfish desires, such as using Mind Control to make herself look even better than she already was. Not only that, she could use forbidden magic without the negative side-effects thanks to a magical charm from her mentor. She eventually does a Heel-Face Turn and joins up with the main group when they save her from the punishment when said charm rots away from overuse.
Alala from Mermaid Melody Pichi Pichi Pitch, but only in the anime. All of the Winged Ones use Magic Music for evil, but anime!Alala goes through the Evil Diva plot and targets civilians to brainwash into fanboyism.
In the manga of Sailor Moon, Mimete of the Witches 5 is an idol and uses her music as a method of brainwashing. It's pretty apt that her counterpart Senshi is wannabe idol Sailor Venus. In the anime, Mimete's a wannabe idol instead of an actual one, and eventually ends up on television. Forever.
Diva from Blood+. Voice could activate Chiropterans; a chiropteran is created by a human ingesting a chemical substance made by the series' Nebulous Evil Organisation. This is almost a subversion, as Diva's voice is "merely" used to activate the evil component in people who ingested it (ice cream bars handed out at an air force base during a tour segment of Diva, as a test case, followed by a world-wide distribution of the chemical, it being included in dozens of popular and generic food items).
Misa Amane from Death Note is an Evil Diva by the second arc. She's a model and actress by day, and by night, she's the Second Kira. Not to mention her room is full of Gothic ornaments and she hangs out with occultist friends.
She does get to sing in the anime, but that may have something to do with her being voiced by Aya Hirano...
Megazone 23's Eve was a not-so-evil version of this; she was the Virtual Celebrity public face of the master computer that maintained the Masquerade for the titular City in a Bottle. A military junta eventually manages to take control of enough of Eve's systems to make her circulate propaganda for the new world order.
Lunar of Seto no Hanayome. She's not straight up evil, per se, but she certainly acts like a bitch most of the time.
EL: the masked terrorist "Gimmick", who is revealed early on to be Reiko, the purple-haired idol singer/assassin seen in the opening of the anime.
Glitter from Hamtaro is not powerful or magical, though she is incredibly bitchy and possessive (also doubles as Nice Character, Mean Actor) - going as far as to drive Laura away from Travis, who she has fallen in love with.
Corona from Kannazuki no Miko, who joins the Orochi after she loses her fame. It doesn't help that she already had very severe issues before that. In the "Where Are They Now?" Epilogue, however, Corona's life is retconned and she's able to be a successful Idol Singer without going for prostitution, presumably because either she managed to do things in another way, or the fans are more appreciative to her.
One of Adam Warren's Gen13 stories had a twist on this: although the song "Happy to Be Happy" caused most of the effects of this trope, it turns out that the singer wasn't responsible. The song itself was a hyper-advanced Ear Worm that was trying to spread itself to gain extra brainpower.
Spider-Man has the D-List villain, The Hypno-Hustler.
Scott Pilgrim has Envy Adams, one of Scott's exes who found massive success in the music world and has transitioned from cute geek girl into full on Alpha Bitch. That said she isn't so much evil as a Jerk Ass with hints of Jerk Ass Woobie.
The titular characters in the Josie and the Pussycats movie become like this, albeit unwittingly. Josie herself winds up getting brainwashed with subliminal messages in order to turn her into a bitchy diva who will break up the band and pursue a solo career (the record company was getting annoyed with Melody and Valerie, and felt that Josie could sell more records on her own). A more conventionally evil example would be Fiona, the diva-ish CEO of MegaRecords, who, while not a singer herself, was the one responsible for putting subliminal messages into her label's music in order to sell consumer products to teenagers. Her real goal, however, was to use the messages to get people to like her and look up to her as a fashion idol, having never gotten over the brutal humiliation she suffered in high school for her bad teeth and her lisp.
Hot Witch Alisa in the movie adaptation of Night Watch. She's played by Russian pop star Zhanna Friske, by the way.
Live Action TV
The would-be assassin in the first episode of Merlin. The singer was a disguise, a glamor, but she still put everyone into a coma-type thing so she could kill Uther and Arthur and only failed due to Merlin's intervention.
Courtney: This goes out to all you robots 'cross the galaxy: It's time for you and me to rise up and strike back! Won't stop until we dominate, won't you feel great When we exterminate, all or-gan-ic life!
Emogame 2 has, as its main villains, The Friends Theory, a band formed by the cast of Friends that uses the power of MTV and Subliminal Seduction to turn America into a nation of soulless, corporate, yuppie zombies.
Linda from Okage ends up doing this, albeit accidentally. She hypnotized the entire city of Madril into loving her singing, not aware that she had somehow absorbed some of Evil King Stan's magic power. Upon finding out what she was doing, she runs off to her dungeon and fights the party because she thinks it is training from her "Coach", Stan. Upon her defeat, the power goes back to Stan, and she cheerfully joins the party.
Experiment 624: Angel from Lilo & Stitch: The Series. She appears irresistibly attractive to all the other experiments and her voice has the power to reverse the morality of every experiment made before her, and thus, only Stitch (626) and Reuben (625) are immune. Probably wouldn't work on 627 either.
Ricky Mathis from Totally Spies! is an unwitting male example, being manipulated by someone who has world conquest as his goal.
Dr. Doofensmirtz from Phineas and Ferb tries to be the Spear Counterpart to this trope in "Bubble Boys". He wears a cowboy hat that makes his voice hypnotic, making whoever is listening to his song want to obey him.
One episode of Animaniacs has the Brain taking on the persona of "Bubba Bo Bob Brain", who has "calculated every ingredient necessary to become a country music superstar".
Pizzazz from Jem qualifies. Vain and egotistical, she wants the whole world to know who she is and half the songs the Misfits sing are either about how great she is or what a bitch she is. Arguably, though, Pizzazz is something of a deconstruction, as her desire for fame stems from a largely loveless childhood and a father who spoiled her rotten.
Sour Grapes from Strawberry Shortcake is a parody of this with her trademark ear-splitting vocalise she uses when she's excited or when she wants to annoy people.