Dark Signer

The Dark Signers are a mysterious group of duelists, whose serve as antagonists to the Signers and primary antagonists for the second arc of Yu-Gi-Oh! 5D's. Their signature cards are "Dark Synchro Monsters".

History
The Nazca Gods, who are evil entities that were sealed in the Nazca Lines by the Crimson Dragon and the Five Dragons, each bore a dark mark on to five individuals, the Dark Signers.

The Dark Signers have repeatedly battled the Signers, who each have a marking of the Crimson Dragon, over the course of 5,000 years.

The Dark Signers serve as gatekeepers to the door that leads to the underworld. This door resides within the first Enerdy generator built, located in Satellite. The Dark Signers plotted to open this gate to release the Nazca Gods. Knowing this Rex Goodwin built the utopia New Domino City away from Satellite and restrict access, between the two cities, so only those left in the Satellite would be harmed when this time came.

After the Crimson Dragon appeared during the Fortune Cup, the Dark Signers began preaching in Satellite that the Crimson Dragon is evil and encouraging the people to stand with them for the sake of Satellite.

Using brainwashed victims, they began targeting the Signers, including Yusei Fudo, who was made duel Dick Pitt and Jack Atlas, who with Carly Nagisa's assistance, dueled Trudge. In both cases the Signer emerged victorious.

Brainwashing
The organization has the ability to brainwash other duelists, by having a black spider latch onto a victim. The victim believes them self to be a Dark Signer, gains the spider dark mark and does the bidding of the real Dark Signers. While brainwashed, the victim's Deck is changed to one more fitting to a Dark Signer.

The spell is lifted when the victim loses a Duel. At this point the spider is ejected from their body and erupts in a powder. The victim's Deck is then restored to normal and they have no memory of what happened while they were brainwashed.

Shadow Duels
When a Dark Signer engages in a Duel, the arena is surrounded in a purple glow and becomes a Shadow Duel. During a Shadow Duel, players suffer real damage when attacked by monsters. The blasts from the attacks are fatal and often cause damage to the surroundings. Kyosuke Kiryu has the ability to create a Turbo Duel shaped like his dark mark.

Dark Synchro Summoning
The Synchro and Dark Tuner monsters are exclusive the Dark Signers. Dark Synchro Monsters are Synchro Summoned by sending to the Graveyard 1 Dark Tuner monster and 1 non-Dark Tuner Monster. The non-Dark Tuner Monster's Level minus the Dark Tuner Monster's Level must be equal to the Dark Synchro Monster's Level (note that the Dark Synchro Monsters have a negative level, something that isn't possible with any other monster in the game).