At first, the title of the season: "Arc-V" may seem like an unimaginative title. However, remember what is a main motive of this season (Pendulum)? Now what does a Pendulum swing in?
In this season, it gives focus to more than just Pendulum Monsters. Why? Because Pendulum Summoning is a PERFECT support to older summoning methods, particularly Synchro and Xyz which need to have the material monsters on the field. Also, because in universe, as of currently, Yuya's Pendulum Monsters are the ONLY ones in existence...at least for now.
Shingo's new deck revolves around destroying Spell/Trap cards with Mobius. He probably intended to destroy Pendulum Monsters.
Every duel disk designs before had clear slots on where to place the monster cards. But this time it's just one continuous piece of light without any markings. It's because if it had the usual slots Pendulum Summon makes no sense. Since Yuya just created the Pendulum Monsters Pendulum Zones shouldn't exist on the dual disk and thus he would have nowhere to place them. If Pendulum Zones were there, then that means Pendulum cards already existed before.
Entertainment Duels are all Action duels, because they are more visually interesting than regular duels. They are way more entertaining to watch.
Which is why the Dark Duelist's duel with Shingo is so much darker, it is was a regular, possibly Shadow, Duel.
In episode 10 Masumi says that Yuzu was blinded by an illusion, could this by foreshadowing that the Dark Duelist isn't real?
Or the illusion could refer to Yuzu's belief that Yuya and the Dark Duelist were one and the same. Yuzu going after the action card's reflection instead of the real thing is also meant to represent that same belief.
Like always, a duelists deck reflects their personality and character.
Yuya uses Entermate monsters; Goofy performing animals about as serious looking as Yuya acts. And they Call Back to the friendship themes, Entermate = Entertainment Mate = Entertainment Friend.
Gongenzaka uses Heavyweight Samurai, a large sized archetype values using defense over offense, similar to Gongenzaka's non-action duelists.
Sora uses Furnimals: innocent looking monsters that have a dark secret to them.
Masumi uses Gem Knights; one of the most noble duel terminal archetypes, and she's the least outright cruel or aggressive of the LDS duelists in the original 3 on 3 duel.
Reiji uses monsters named after conquerors, reflecting his power as CEO of LDS, with its apparent global monopoly of Duel Monsters, which of course makes the world go round, as well monsters named after astronomers, reflecting his intellect.
Why is Masumi the most concerned about Professor Marco? Because he is the fusion course teacher, which means that she is the closest to her, and likely even taught her how to duel.
At first the mentions of Fusion, Synchro and Xyz Summons courses at LDS where welcomed for being first time an installment makes reference to the summons from the other series, but since the appearance of Sora with his Fusion Summons and now the Dark Duelist with the Xyz Summon has started to raise a few eyebrows over the fact that everyone seems really surprised at anyone who isn't a student of LDS knowing how to make those summons, while this is kinda justified for the Pendulum Summons because Yuya pretty much discovered it, the fridge logic kicks in when you notice that they could simply read the instructions which are all written on the freaking cards.
Well, not on the cards, but it is in the rulebook, and so the basic method should be covered in Dueling 101. However, it seems that extra deck cards seem to be harder to get in the show; professional duelist Jack Atlas used only 5 himself (Red Dragon Archfiend, Majestic Red Dragon, Red Nova Dragon, Exploder Dragonwing, and Crimson Blader), and he was a champion. Yuma never had one until the start of his series, and Yuzu's father has never Xyz summoned either. It's possible that they are something of a status symbol, and so are more likely to be in the hands of a better equipped school.
And yet Yusei has 15, and notably a few even when in the satellite, where only cards thrown away go.
Admittedly when I wrote that I still haven't watched the 8th episode, and apparently LDS has been indeed hoarding all these summon types and (I assume) the cards needed for them. However while It's understandable the whole status thing and the cards not being easy to find, there's still the issue of people knowing nothing but the summon's name and just having an apparent ignorance of what those summons even consist about, It's like you can never even played the game and still theoretically understand how certain summon is made by following the events or keeping track of your favorite duelist, specially if in the YGO verse pro duelists are treated as huge stars.
On the above point, if we focus simply on the Synchro Monsters pre Meklord, all but Stardust (which is implied to be soul bound to him or something) require specific tuners. Monsters like that are generally seen as less valuable than more splashable synchros, such as the ones Jack uses.
So, Action Duels are created by making solid matter, so that means that players can be physically damaged by cards, right? So if someone is using a deck full of torture cards (say, Marik, in the original show) they can actually do some serious harm to a player. How on earth would anyone sign off on turning holographic images of vicious dragons and giant robots and dark wizards into solid things? Think of how many people could die or get seriously injured just practicing with their cards in a duel and accidently blowing themselves up.
Imagine if someone got attacked directly by a monster with a sword or a gun...
Basically, with Action Duels, everyone has access to their own Shadow Games. And they play them. For fun.
One teased by the show itself. Not long after Masumi defeats Yuzu in their duel, belittling her as she does so, a Professor from her school disappears who she seems to be quite close with. Did the Dark Duelist feel like dishing out some Disproportionate Retribution?