The regular "D/D" monsters seem to be based on different figures and monsters from Western mythology, while the "D/D Savant" monsters are references to great natural scientists from Western history.
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 "Dark Contract" cards resemble business contracts, and the names of "D/D/D Human Resources" and "Contract Laundering" reference like-named company practices.
Additionally, some of the archetype's boss monsters such as "D/D/D Doom King Armageddon" feature a pun in its Japanese name, such as "Great Des (Death) King" being 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"/"D/D/D Wave Oblivion King Caesar Ragnarok", "Oblivion King", which is scripted as "Kaichiō", a homophone for "Chairman".
So far in the ARC-V manga, the "D/D" monsters appear to be demons with a mechanical, scientific theme (distinct in design to the "D/D Savant" monsters) and have equipment like scales or microscopes instead of faces.
One can start off by using "Savant Kepler" to search for "Dark Contract with the Gate", which in turn can search the combo starters of either "Swirl Slime" and "Necro Slime" and the finisher "D/D Lamia". The Slimes are Fusion enablers (hand and GY, respectively) and Lamia is a level one Tuner Monster.
"Flame King Genghis" (a Level 6 Fusion Monster) can combo its effect with the similar "D/D/D Gust King Alexander" (a Level 7 Synchro Monster) to climb to Level 8 at least, using a Level 1 Tuner such as "Lamia" to summon "Crystal Wing Synchro Dragon" (which has monster effect negation, destruction and ATK gain) and "Cursed King Siegfried" (which can negate any Spell or Trap at Quick Effect speed) for two of some of the most powerful negation effects.
Either the effect of "Lamia" or "Siegfried" can used to bounce or negate without destroying to avoid the cost of the "Dark Contract" cards for a turn, or use the effects of "Oracle King d'Arc" (which turns effect damage into gain LP) and "Rebel King Leonidas" (which prevents effect damage) to disable the LP payments permanently. Neither of these effects interfere with each other, allowing the player to continuously gain LP but also avoid effect damage should "d’Arc" be destroyed or have its effect negated.
Additionally, the Deck has access to many cards that can recycle resources from the Graveyard, face-up from the Extra Deck, and the Pendulum Zones, such as "Lilith", "Oblivion King Abyss Ragnarok" and "D/D/D Human Resources".
With the release of Structure Deck: Pendulum Domination, "Savant Copernicus" and "Savant Newton" provide more consistent Pendulum Scales than "Savant Kepler" and "Savant Galilei". "Copernicus" has the bonus of dumping "D/D" cards from the Deck to start combos, whereas Newton can discard itself to add a "Dark Contract" card or a different "D/D" monster from the Graveyard. "D/D Orthros" is a reusable Tuner monster, by virtue of also being a Pendulum Monster, to make Synchro Summons easier to execute. "Dark Contract with the Yamimakai" can set the Pendulum Scales from the Graveyard or Extra Deck to start Pendulum Summoning.
The following Decklists may or may not contain copies of cards that exceed the maximum number allowed by the current Forbidden & Limited List. These should not be changed, as these Decklists are copied verbatim at the time they were published.
Because this Deck focuses on swarming to push the game, cards that can disable or counter swarming or searching, like "Fossil Dyna Pachycephalo" or "Thunder King Rai-Oh", can greatly hinder this Deck. Additionally, the archetype's synergy with the "Dark Contract" archetype provides a weakness to Spell/Trap removal, as well as a dependence on cards that mitigate the damage from the "Dark Contract" cards.