Monster: Yu-Gi-Oh!

"I am a thief and a stealer of souls, and I have done terrible things in my quest to possess the Millennium Items. You DO remember the legends, don't you?"
Yami Bakura (while possessing the real Bakura) to Yami Yugi, Anime Series, "Evil Spirit of the Ring"

Complete Monsters from the Yu-Gi-Oh! franchise.
Manga and Second Series Anime
  • The Spirit of the Millennium Ring, known as Dark Bakura (Yami Bakura)]], was the longest running antagonist of the series, and one of its worst, though his actions between the manga and anime were different.
    • In the manga, Dark Bakura was with Ryo Bakura for a long time before he moved to Domino City. Whenever any of Bakura's friends tried to play games with him, Dark Bakura would trap them inside of RPG figures, putting them into comas. When Yugi and his friends came over to play the Monster World RPG game that Bakura himself created, Dark Bakura trapped them inside over the course of the game and tried to kill them. After this, he fakes a Heel-Face Turn and gets the gang to believe that he's trying to help them (though they don't trust him) and then kills Pegasus and steals his Millennium Eye behind their backs. During Battle City, he stabs himself in the arm and then reverts back to normal Bakura so that Marik can gain the groups trust and then murders Ghost Kozuka after a duel to take his Puzzle Card. In the final arc, Dark Bakura is revealed to have manipulate his host into constructing an RPG of Atem's final battle, in which the RPG figures are implied to be sentient, to summon Zorc Necrophades, who will then proceed to destroy the world, again if he wins the game against Dark Yugi. He duels Jonouchi and Yugi at two separate occasions and nearly kills them both.
    • In the anime, the Spirit of the Ring was possessing Yugi's friend Bakura for almost the entire duration of the series. During the Duelist Kingdom arc he traps Yugi and his friends within the card game, resulting in their being sent the graveyard if defeated. He subsequently tries to bodyjack Mokuba Kaiba, and rips Pegasus's Millennium Eye out of his eye socket, leaving him in a coma. During Battle City, he infiltrates the tournament and sends Bonz, Zygor, and Sid to the Shadowrealm, then tries to do the same to Yugi and Yami. Failing, he returns in Season 5 as The Big Bad. Outing himself as an agent of Zorc Necrophades, The Spirit of the Ring repossesses Bakura, and sets in motion a plot to bring about The End of the World as We Know It. He kidnaps Mokuba to force Kaiba into a Shadow Game, then traps the cast in the Memory World, where he can control their lives, possessing Tristan and his own past self, Thief King Bakura, in the process. Eventually pulling a You Have Outlived Your Usefulness on his own past self, The Spirit of the Ring unleashes Zorc in the past, while taking on Yami in his final Shadowgame in the present, with the intent of making the world bow down to his dark god.
  • Dark Marik (Yami Marik) is the twisted split personality who drove the real Marik off the deep end in the first place. Seizing control of Marik's body during his childhood, he killed their abusive father, and then tried to kill their adoptive brother, who had been keeping Dark Marik locked up. This failed, and Dark Marik bided his time, gaining strength, and driving Marik to further and further acts of cruelty in his quest to kill Yugi and/or Take Over the World including, but not limited to, kidnapping, Mind Rape, brainwashing, and attempted murder. Resurfacing when Marik's adopted brother was defeated in the Battle City semifinals, Dark Marik exiled his better half from their shared body, and then decided to personally screw with everyone for no reason. He engaged Mai Kujaku/Mai Valentine, the aforementioned Dark Bakura, and Katsutya Jonouchi/Joey Wheeler in a series of sadistic Shadowgames, with Mai experiencing imaginary but extremely painful wounds/losing memories whenever a monster was destroyed, the Bakura/Spirit of the Ring lost parts of his body, and Jonouchi/Joey felt extreme pain when a monster was destroyed/lost life energy. The games eventually saw Mai trapped in her own mind slowly dying, Bakura completely vanishing, and Jonouchi/Joey in a coma (in the dub, all three were sent to the Shadowrealm). He also made several attempts on the lives of his sister and comatose adoptive brother. This all culminated in a final battle against Dark Yugi/Yami, during which he arranged for any damage the two of them incurred to be suffered by their better halves, Marik and Yugi, nearly killing them both. An Ax-Crazy Combat Sadomasochist with omnicidal designs on the cast and/or world, Dark Marik left the cast in shellshock.

Yu-Gi-Oh! GX
  • Brron, Mad King of Dark World, is demented and sadistic, ruling the Spirit World as its vile dictator and being responsible for its deplorable state and the oppression of its denizens. His right-hand man, Zure, oversaw Brron's will, detaining anyone who defied him in internment camps while killing duelists who could be threats to him. The executions occurred at his fortress and involved releasing monsters at disarmed duelists while Brron himself and his minions watched the spectacle. After learning of Jaden's presence in his domain, Brron orchestrated a plot that involved turning Jaden evil by sacrificing all of his friends one by one with his set of "Wicked Doctrine" cards to create the "Super Fusion" card. After his defeat, Brron, before dying, mocked Jaden by saying that he would never see his friends again before dying.

Yugioh 5 DS
  • Divine/Sayer is the leader of a group of duelists training to control and harness their psychic abilities in order to turn them into soldiers of war against the rest of humanity. His earliest duelist, Toby Tredwell, was unable to withstand the procedure meant to test his abilities. Believing him to be weak and useless, Sayer ordered the intensity of the electric shocks to be amplified, which caused the young boy's death. He also does his best to keep his prized duelist Akiza secluded from anyone outside the Arcadia Movement to keep her full of hate and resentment at the world for his goals, as well as hide his own secret motives. To this end, he gasses Luna, Leo, Yanagi and Bolt Tanner when they come to him for aid against the Dark Singers. Then he threatens Leo's life in a psychic duel to test if he has powers like his twin sister Luna. Later that day he has another Psychic duel with and murders Carly Carmine by sending her through a window with a direct attack, kick-starting her rebirth into a Dark Signer. He then returns from his Disney Death at the hands of Carly, posing as a security agent to attack Yusei and Mina. Sayer states that anybody who falls prey to him will simply follow his orders and nothing more, as he takes full advantage of that individual's weakness, just like he did with Akiza.
  • Lotten/Lawton is a tyrant lording over a small western style town called Crash Town, who forces those he's defeated to join him or face slavery in the mines. He gets into a match with Yusei while Yusei and the gang are trying to escape the mines, but before it can be decided, he throws a stick of dynamite at Yusei, Kalin, West and Nico that results in cave-in. When it explodes, Yusei and Kalin fall off the mountain, while Nico and West are unconscious on the ground. Lawton takes them back to Crash Town, renaming it Lawton Town after Barb and he double-cross his brother Malcolm. Later, not satisfied with the number of workers in the mines, he and Barb begin forcing their henchmen to Duel for their survival, which is stopped by Yusei and Kalin. Once he does start to lose his 2-on-1-handicap match against Yusei and Kalin, he quits the duel and tries to run away, but not before he abandons Barb to her fate and set off explosives in the town.

Video Games
  • Yu-Gi-Oh! Forbidden Memories: Heishin is an Evil Chancellor and Evil Sorcerer of Ancient Egypt. As soon as he gets the ancient power of the Millennium Items, he attacks the palace with his soldiers, killing various people (including the Pharaoh and his wife) and mortally wounding Simon Muran, the Prince's tutor. When the Prince tries to escape, he threatens to kill him if he doesn't give him the Millennium Puzzle. The Prince shatters it, and is transported inside of the puzzle to the present day. When he returns, he finds that Heishin has destroyed much of Egypt and Simon Muran has died from his injuries. After defeating Heishin's top mages, he finds Teana has been kidnapped and is having her life threatened in an attempt to lure the Prince into a trap to kill him, but this is stopped by Seto, Heishin's own henchman, who sets her free and ends up being The Starscream. Heishin obtains the Millennium Puzzle and summons the Dark God, Darknite, and commands him to destroy the world and make him a god, to which Darknite responds by killing Heishin. Petty, selfish, and so obsessed with power that he'd attempt to murder underage teenagers in his pursuit of it, Heishin was a monstrous individual.