Darkrai

Although in the anime Darkrai is seen as a hero, in some video games he is a villain bent on ruling the whole world of Pokemon and making it a world of darkness. His most important role as a villain is in Pokemon Mystery Dungeon 2: Explorers of Darkness and Explorers of Time, where he is the true main antagonist of both games. Apparently it is not known if he is a different Darkrai or the same one, and with this to also add, the anime and games contradict one another and with this confuses many people.

Pokemon Mystery Dungeon 2
Though Darkrai is normally a well meaning being, in the Pokémon Mystery Dungeon series of games, mainly Pokémon Mystery Dungeon; Explorers of Time, Darkness, and Sky, Darkrai serves as the true main antagonist and is a force of pure evil.

Pokemon Ranger: Shadows of Almia
Darkrai is the final boss in the video game; Pokemon Rangers: Shadows of Almia, though he does not initially appear as a villain in this game, but must be stopped from engulfing Almia into darkness. Darkrai's power is exploited by Blake Hall, the main antagonist of the game. Blake uses Darkrai and the black crystal that Darkrai protects to fuel his machine. But when a malfunction occurs, Darkrai becomes enraged, becomes even more powerful, and engulfs Blake into a black hole, which was Darkrai's Nightmare technique. However, when the hero uses the power of the red, yellow, and blue crystals collected earlier in the game, Darkrai is able to be stopped.

PokePark 2: Wonders Beyond
Darkrai is the true antagonist in PokePark 2: Wonder's Beyond. He wanted all the Pokemon that lived in the PokePark to remain in Wish Park, all because he was lonely. While his intentions weren't really that evil, he nearly destroys both worlds in the process as well as possessing several Pokemon such as Zoroark, and Piplup, and nearly wiping out the memory Snivy, Tepig, and Oshawott of Pikachu.

Capturing Piplup
After Pikachu and his friends defeated Cofagrigus, Darkrai attempted to keep Pikachu, Oshawott, and Piplup in the Wishland. Pikachu and Oshawott managed to escape, but Darkrai captured Piplup.

Darkrai Revealed
After Haxorus was defeated by Pikachu and his friends, both he and Hydriegon found out that they were tricked by Gothitelle. Just when they were about to confront her, Darkrai attacks them, knocks them out, and reveals himself to the main heroes. He told Gothitelle to retreat to the final Wish Park Zone.

Breaking Pikachu
When Pikachu and his friends reached the palace, Darkrai possesses Piplup and convinces him to fight his friends. When Piplup was defeated, he regain full control and ran away. Just then Darkrai, along with Gothitelle, Gothorita, and Gothita teleported in the palace. Darkrai used his powerful psychic abilities and wiped out Snivy's Tepig's and Oshawott's memory of Pikachu. He then teleported Pikachu into the center of the square. Feeling depressed, Piplup appears and tells that there's still hope. So Pikachu went towards the Cove Area to find Oshawott, Meadow Area to find Snivy, and the Crag Area to find Tepig, as well as getting their memory back.

Confront Pikachu and Friends
After Pikachu found all four of his friends, they went to Wish Park and confronted Darkrai. After he was defeated, Darkrai absorbed all of his power and grew rough 10x his size. After being defeated again, He saw the Dark Vortex. He realized that this was all his doing, so he decided to scarifice himself to protect the Wish Park.

Darkrai's Rescue
Despite Darkrai doing for harm then good, Pikachu and his friends were wondering about Darkrai, and if he was still alive. So they went on a search for Darkrai. With the help of Reuniclus, Tornadus, Thundurus, Landorus, as well with Reshiram, and Zekrom, they were able rescue Darkrai. Despite of him doing more harm then good, Darkrai was asked by Pikachu and his friend to be his friend. Since they forgiven Darkrai, Darkrai accepted their offers.

Minions

 * Gothitelle (Right-hand, and possible Love interest)
 * Gothorita
 * Gothita
 * Sigilyph
 * Chandelure
 * Haxorus
 * Hydreigon (Redeemed)
 * Cofagrigus
 * Yamask
 * Litwick
 * Lampent
 * Arbok
 * Rhyperior
 * Magmortar
 * Aggron
 * Magcargo
 * Mismagius

Super Smash Bros Brawl
Though Darkrai doesn't appear in Super Smash Bros Brawl, he does appear as one of the trophies.

Super Smash Bros 4
Darkrai makes his appearance in the video game; Super Smash Bros for Wii U and 3DS. He appears as one of the Pokémon emerging out of a Pokéball, or Master Ball. When Darkrai emerges from the Pokéball, he'll unleash a Dark Void. Anyone who comes in contact with the Dark Void will be put to sleep, and those that are asleep, will be dealt with heavy damage due to Darkrai's Bad Dreams ability.

Trivia

 * Though a Dark-type Pokémon, Darkrai can walk through walls in the Mystery Dungeon games even though he isn't a Ghost-type.
 * Thought Darkrai is genderless in the main game series, he is regarded as male in other game series since his archenemy Cresselia's gender is female.
 * Darkrai is the first known Dark-type Legendary Pokemon, with Yveltal as the second.
 * He is perhaps the darkest version of Darkrai.
 * In the side quest of the games, Darkrai can walk through walls, despite not being a Ghost-Type Pokémon.
 * Though genderless in the main games, Darkrai is referred as a male in the series.
 * According to Palkia, Darkrai is not killed as the blast gave him amnesia, similar to that of the player's. With his thoughts of world domination, and plunging the world into darkness and nightmares erased, Darkrai is left to wander the world. He can be encountered & recruited in any certain dungeon if the player brings a Secret Slab or Mystery Part. It's up to fans to decide whether he redeems or not after his recruitment.
 * Among Darkrai's minions, Arbok is the only Pokémon who cannot be encountered in the floors of Dark Crater.
 * This Darkrai has many similarities with the Joker from the Nolanverse:
 * Both made their debut in the second installation of their respective series.
 * Both have manipulated individuals and events to their own gain.
 * Both have drove an individual into becoming evil and insane (Darkrai drove Dialga into becoming Primal Dialga, while the Joker drove Harvey Dent into becoming Two Face).
 * Both desire absolute destruction and chaos of their worlds, though Darkrai was planning to rule the tattered remains of its world, while the Joker cause chaos and destruction simply for entertainment.
 * Both had their minions help them against their fight with the heroes (Darkrai had his fellow Pokemon and the Joker had his dogs).
 * Both had backup plans should their original plan fail (Darkrai would escape through the dimensional hole, while the Joker was going to blow up the two hostage ships anyway).
 * Both survived their fight against the protagonist but not without suffering some form of punishment, despite it being small compared to the damage they caused (Darkrai suffered amnesia, while the Joker went to prison).
 * Both of their action led to devestating consequences in the future.
 * Darkrai also has similarities to Tobi from Naruto:
 * Both manipulate someone to further their plans (Primal Dialga for Darkrai, Sasuke Uchiha for Tobi.
 * Both change considerably after having their defeat.
 * Darkrai also has similarities with Dimentio from Super Paper Mario:
 * Both made their reveal as the true main villain near the end of their respective games.
 * Both have manipulated events and individuals behind the scenes, including the false antagonists.
 * Both have broke the minds of someone to further their plans (Dialga for Darkrai, Fracktail for Dimentio).
 * Both don't care if their actions cause the world to be in ruin so long as they get to rule it in the end.
 * Both have offered the heroes to join them.
 * Both tried to get rid of the heroes once they are of no use to them.
 * Both used individuals to help them get rid of the heroes (Darkrai used his minions, while Dimentio used Luigi).
 * Both had backup plans should their original plan fail (Darkrai would escape through the dimensional hole, while Dimentio would use the remains of the Chaos Heart to destroy reality).
 * Both are the most cunning and powerful villains of their respective game series.
 * Both are also the darkest and evilest villains of their respective game series.
 * Both debut in a spin-off of a main video game series, Mario and Pokemon respectively.
 * Intersestingly, both of those game series come from Nintendo.