A Turbo Duel, known as Riding Duel (ライディングデュエル Raidingu Dyueru) in the Japanese version, is a type of Duel which is only played by either using a "Duel Runner" or a "Duel Board" in the Yu-Gi-Oh! 5D's series and in the Yu-Gi-Oh! ARC-V series. It can be activated without the consent of the opponent by activating the Field Spell "Speed World", "Speed World 2" or "Speed World Neo", seeing as how everyone who Duels on the road is a candidate for play. Usually when a Turbo Duel starts in a stadium, an MC will shout (Japanese version only) "Riding Duel! Acceleration!".
Turbo Duels came with the advent of Ener-D, the power created from the positive energy of Dueling that powers the city's technology, including their vehicles. Turbo Duels were created when KaibaCorp thought to invent a sport that took advantage of an Ener-D-powered vehicle, as it adds many new dynamics to Duels.
The exterior element of movement is the key idea behind Turbo Duels, as it adds an unexplored element of dodging, riding skill, intimidation and imagination. Turbo Duels are much more intense than regular Duels, from not only the danger, but being as that the Duelists are connected to The World of Speed, the Duelists emotions are connected to each other. Dodging attacks also seems to be an aspect of Turbo Dueling, because you have until the attack connects to activate a trap card in response, as evident by Duelists who avoid being physically struck by attacks even in Duels where they can't be hurt, than activate a trap after they dodge. This adds the element of movement to a Duel where it wasn't present before.
Turbo Duels add the potential for new rules that take advantage of the Duel Runners on which players ride, as shown by the Yu-Gi-Oh! 5D's tag team rules and the exterior element of optimizing your Duel Runner adds a new level of skill and culture to the Duels. The varying distance between the players adds the element of keeping up with your opponent to better react to their moves, which adds another element of movement to Dueling. Turbo Duels make Dueling into a sport akin to jousting, especially in that the most famous Duelists Turbo Duel in the rich part of the city.
In the manga, Rex Goodwin explains that in ancient times Turbo Duels were rituals conducted since ancient times, and were designed to fight and seal the darkness. In such times, they were conducted with horses and stone tables rather then Duel Runners and cards. The Duel Dragon cards were specially designed for such rituals. It was later revealed that a Turbo Duel between a Duel Priestess and a Duel Priest was an annual religious event, which, depending on the results, could awaken the Ultimate God. Rex and the Skeleton Knight then conduct the event once more in the present time, using Akiza Izinski and Sect Ijuin, with a modern Turbo Duel.
When a Duel Dragon card transported Yusei Fudo and Crow Hogan to ancient times, Yusei underwent a ritual to obtain the card - a Turbo Duel against a Priest of Light. Yusei used his "Lightning Warrior", while the priest used his "Stardust Spark Dragon", in a One-Shot Run. Yusei eventually accepted the dragon's blow and concluded the ritual, obtaining the card.
At the start of a Turbo Duel, the Field Spell "Speed World" (later "Speed World 2") is automatically activated. These cards are unique Field Spell Card that changes the gameplay of normal Duels to create a Turbo Duel with additional rules and gameplay.
When "Speed World" is activated, the Duel field is covered in a purple dome (no purple dome with "Speed World 2", although the scenery does change sometimes). Some Duel Runners have the ability to force other nearby Duel Runners into a Turbo Duel by activating the other player's "Speed World" card forcefully.
Normally, to allow a player to focus on a Duel, when a Turbo Duel is engaged, the Duel Runners enter autopilot. This autopilot can be toggled on or off to add to the challenge by requiring the Duelist to steer the Duel Runner manually while handling the cards. Auto-pilot is not applied when using Speed World 2.
During each of either player's Standby Phases, 1 Speed Counter is placed on both player's "Speed World"; although in the anime a Speed Counter is not placed on the first turn, in video games featuring Turbo Duels, it is. There are also cards which can either decrease or increase the number of Speed Counters on "Speed World".
There are even cards that can prevent either player from accumulating Speed Counters. When you take damage, for each multiple of 1000 damage you take, you lose 1 Speed Counter. With "Speed World 2" however, you don't.
"Speed World" also inflicts 2000 damage to a player's Life Points whenever that player would activate a non-"Speed Spell" Spell Card in a Duel. The video games Stardust Accelerator and Reverse of Arcadia possess the characteristic of restricting this particular rule; as the condition when editing your Deck for Turbo Duels, is that it may not contain any non-Speed Spell Spell Cards. This is because "Speed World" instead prevents either player from activating non-"Speed Spell" Spell Cards.
As for the anime series itself regarding this subject, this particular rule doesn't occur, as it has been stated multiple times that one cannot activate Normal Spell cards in Turbo Duels. However a few characters are seen with Normal Spells in their hands, like "Reload", for what reason is not explained.
In the manga, "Speed World" does not exist. Instead, additional rules are added which have to do with the riding itself. For example: the player loses the Duel if their Duel Runner stops and can win instantly if they cross the finish line first.
It should be noted, however, that there are no Equip-Speed Spell cards, so cards like "Power Tool Dragon" or "Vylon Delta" would be almost worthless. Also, there are no Continuous-Speed Spell cards, meaning that cards like "Hamon, Lord of Striking Thunder" would not be able to be used normally without the help of the "Crystal Beasts". There were no Ritual Spell cards until Yu-Gi-Oh! 5D's World Championship 2011: Over the Nexus, so Ritual Monsters had no use in a Turbo Duel until then.
Speed Counters are only used in Turbo Duels. This kind of counter is used by "Speed World" and it enables both players to gain Speed Counters on either of each player's Standby Phase of the turn (max. 12).
Speed Counters affect the actual speed of your Duel Runner. Most Speed Spells requires a minimum number of Speed Counters to be present and some also require you to pay counters. These counters are referred to on the Duel Runner's display monitor as "SPC".
Turbo Duel specific cards
In most cases, this is simply having enough Speed Counters, though there are other requirements based on the number of counters you or your opponent have. Some Speed Spells can be activated without any requirement or cost, but the majority do need requirements.
Some cards in the anime can only be used in a Turbo Duel, due to its relation with Speed Counters or Speed Spells, however it is mentionable that these cards also appear and can be used in some video games.
Turbo Duels were reintroduced in ARC-V, in the Synchro Dimension.
Turbo Duels in ARC-V do not use Speed Spells or Speed Counters, but they do use a new version of "Speed World" called "Speed World Neo". Additionally, Action Duels have been combined with Turbo Duels adding more dynamic to the Duel, as Action Cards can be used during the Duel.
According to Frank, Tarren and Crow, the Turbo Duels were created by Commons as a way to outwit the Topsiders. However, Sector Security formed the Duel Chasers in order to stop the Commons who Turbo Dueled in New Domino City and the Tops started to broadcast the pursuits as entertainment for them.
Field Spell Cards can be used in addition to the active default Field Spell Card of a Turbo Duel; however it is unknown whether or not two players can control Field Spells at the same time.
In the manga (as well as occasionally implied through actions in the anime), a Duelist can speed up to make more of a physical impact with their monster's attacks. This is due to the use of something called Sense (Feel in the Japanese version), which is a magic that carries a Duelist's emotional intent with their monster's attack, and turns it into an energy which affects the opponent when struck. In the anime, it is possible to attribute this sort of phenomena to Ener-D instead.