D/D

"D/D" ( DīDī), known as DD in the English manga, is an archetype used by Declan in the special Yu-Gi-Oh! ARC-V chapter and anime. It is supported by its own sub-archetype "D/D/D". So far, they are all DARK Fiend-Type, except for the Extra Deck monsters, which have a different Attribute each.

Design
The regular "D/D" monsters seem to be based in different figures and monsters from Western mythology, such as Chevaliers, Lilith, Ogres, Cerberus, Pandora, etc.

In contrast, the "D/D/D" sub-archetype features a distinct design style from the rest of the archetype, with many of its members modeled after famous conquerors from world history.

Taken together with its subordinate and sub-archetypes, the "D/D" archetype features a mild "business" sub-theme (probably to fit the profession of their owner in the anime), with many support cards referencing elements of modern big business. For example, the "Covenant" cards resemble business contracts, and the names of "D/D/D Resource Management" and "Lease Laundering" reference like-named company practices.

Additionally, the boss monster for the entire archetype, "D/D/D Hell Armageddon the Cruel End Overlord" features a pun in its Japanese name– "Great Des (Death) Lord" is scripted as "Shiiō", a homophone for "CEO". A similar pun can be found in the Japanese name of "D/D/D Oblivion King Abyss Ragnarok", "Destruction Lord", which is scripted as "Kaichiō", a homophone for "Chairman".

Etymology
According to Sora Shiun'in, "D/D" is short for "Different Dimension" (ディファレント・ディメンション Difarento Dimenshon).

Playing style
"D/D" monsters revolve around utilizing efficient searching and swarming effects to Summon Fusion, Synchro, Xyz and Pendulum Monsters, as well as manipulating "Covenant" Continuous Spell and Trap Cards to reap their benefits and evade their drawbacks. They also include numerous effects to recover lost "D/D" and "Covenant" cards from the Graveyard, and to add them from the Deck to the hand.

This deck's primary playing style is massive summons using "Temujin" and "Alexander" and high-level Synchro monsters with "Night Howling" (It should be noted that the "D/D" monsters should preferably be Special Summoned for attacking with "Alexander" or "Temujin," not with "Night Howling," as that reduces the Summoned monster to 0 ATK). One can easily get 7000 ATK damage on the board. Since Pendulum Monsters counteract putting them into the Graveyard from the field, it is best to use "Covenant with the Valkyrie," "Covenant with the Swamp King," "Kuribandit", "Hand Destruction" and/or "Needlebug Nest" to put them in the Graveyard from the Deck and hand.

In order to accomplish a large swarm a somewhat strict but manageable setup is required. First one should Fusion Summon "Temujin" (without Normal Summoning) through "Swamp King" which can also banish materials from the Graveyard (a Level 4 monster should always be in the Graveyard. Next Normal Summon "Night Howling" and use its effect to Special Summon 1 D/D from Graveyard, preferably a "D/D Lilith" in the Graveyard as "Night Howling" can revive her and make the most of her recycling effect, immediately after Synchro Summon "Alexander". Once this happens Temujin can use its effect to Special Summon 1 "D/D" monster from Graveyard, and then Alexander can use its own effect to revive a Level 4 or lower "D/D" (one of which should be a Level 4 monster). Finally if "D/D Cerberus" is on a Pendulum Scale, it can turn any non-level 4 monster into a level 4 which can be used to Xyz Summon "Caesar". This combo has many variations however, as "Temujin" unlike "Alexander" can Special Summon ANY "D/D" monster, regardless of level, including a copy of himself which can open Rank 6 plays, which can expand the horizons of the Deck and create several combinations. By emplyong cards such as "Call of the Haunted", one can reinforce the swarm much more without needing to use "Night Howling" effect, thus enabling its user, several more options. Although most of this swarming can only be done if one can access Fusion Summon through "Swamp King" and acquire the assets needed through "Covenant with the Hellgate", which can often require a turn or two, leaving the combo vulnerable to Spell/Trap removal at some point, thus one must also be patient and know when to explode.

The Deck also has considerable draw power, putting good use to cards such as "Hand Destruction," "Magic Planter," "Lease Laundering," and "Allure of Darkness." Although "Magic Planter" works solely with Traps, if the player incorporates other helpful Continuous Traps such as "Fiendish Chain" or "Call of the Haunted" (the latter which is most useful due to swarming) it can help in reaping several benefits, also "Emergency Provisions" can also be used to regain lost Life Points and stay in the lead.

Another strategy involves "Dark Snake Syndrome": because of the presence of cards like "D/D/D Rebellious Overlord Leonidas" and "Lease Laundering" to reduce the negative effect of the "Covenants", you will be able to prevent the negative backfire of "Syndrome" and inflict tons of effect damage to your opponent. If "D/D/D Oracle Overlord D'Arc" is included, you can gain LP while reducing your opponent's.

Because most of the Deck's bosses are Level 7 monster such as "Alexander" "Leonidas" "Kaiser" and "D'Arc", the Deck can also incorporate Rank 7 monsters into their assets, It should be noted however that if the effect of "Night Howling" is used, this cannot be done in the same turn as there are currently no Rank 7 Fiend-Type monsters.

Since the Deck features many high level Main Deck monsters, it is capable of huge raw power, although it can often be detrimental if one cannot summon those monsters as currently, the only ways to Summon them quick through Pendulum Summon involve "D/D Magical Astronomer Kepler" and "D/D Proud Ogre" that have high scales, although the former is not very stable as a Pendulum Card due to its reducing scale, while the latter cannot summon "Hell Armageddon" or "Abyss Ragnarok". Because of this a recommended but not obligatory approach is to employ as fewer high levels as possible, leaving "Proud Ogre", "Leonidas" and "Galilei" the most useful for the Deck, largely since "Proud Ogre" can Pendulum Summon "Leonidas" and lower level monsters and provide an attack boost, "Leonidas" is mandatory due to its effect that circumvents the "Convenants'" LP fee as well as having large stats and "D/D Magical Astronomer Galilei" which can be used to protect cards by returning them to the hand, serving as Fusion fuel as well. While "Abyss Ragnarok" and "Hell Armageddon" can be helpful, it is unwise to run them in high numbers as they are difficult to summon, and are best used on the "Pendulum Zones", the former can help in swarming while the latter can provide the large boost of 800 ATK which can help many monsters in defeating difficult threats. "D/D/D Conquest Overlord Kaiser" is the least helpful since it is not a Pendulum Monster and his effects are derived from Pendulum Summon. Although it has huge offensive abilities it can often be left unused, also destroying your own "Convenant" cards for his effect can be a several drawback if the OTK is unsuccessful.

Weaknesses
"D/D" decks have a few major weaknesses. First, this deck focuses entirely on swarming to push the game, so decks that disable or counter swarming (like "Fossil Dyna Pachycephalo", "Black Horn of Heaven", etc...) can greatly hinder this deck. It also has a built-in weakness through the "Covenant" cards themselves. Each new covenant card provides a great boon, at the cost of an additional 1000 damage each turn, which can build up damage fast if not controlled. However, these costs can be mitigated with "Lease Laundering", "D/D/D Oracle Overlord D'Arc", and "D/D/D Rebellious Overlord Leonidas". Finally, the "Fire Hand"/"Ice Hand" combo poses a great threat to this deck, able to completely break a "D/D" player's field presence in one fell swoop. Also, "Skill Drain" can slow a "D/D" deck to a crawl, given that most of its best effects activate on the field.