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.
And now, Yuya is using Fusion in tandem with Pendulum. Whoever made this realisation, you predicted a crucial plot point well ahead of its revelation.
Sawatari'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 Sawatari is so much darker, as it 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 duelist's 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 Superheavy Samurai, a large sized archetype values using defense over offense, similar to Gongenzaka's non-action duels.
Sora uses Furnimals: innocent looking monsters that have a dark secret to them.
Hokuto uses Sacred/Constellars referring to his stellar performance with a 40 duel win streak while taking no damage. His name also refers to the Big Dipper, a well-known constellation.
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. Her father was also a jeweler, and her name means beauty/purity.
Yaiba uses X-Sabers, appropriate for his Kid Samurai characterization. His last name means blade.
Reiji uses monsters named after conquerors, reflecting his power as CEO of Leo Corporation, 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.
Michio uses Cookmates, being a masterful chef.
Kyuando uses Quiz monsters, and cards that force his opponent to answer questions so that he can react accordingly to outwit the opponent, reflecting his intellect.
Kurosaki uses Raid Raptors, an archetype of cybernetic birds of prey, representing how he hunts the members of LDS to find Ruri, and how his mission has blinded him to everything but itself, leaving him cold just like his mechanical monsters.
Reira's deck has a camara motif and relies on spell cards that can duplicate an opponent's monster. This shows that all he actually has no spark of his own and all he does is in order to be another prodigy like his brother to please his mother, leaving him traumatized. The card that nullified the effects on Ayu's side show that, from his point of view, the world is a cold and grey place.
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.
Confirmed in Episode 21. With the addition of Masumi having a crush on Marco.
Yuya commented that the leader of the Entermate/Performapal monsters is Hammer Mammoth. This makes sense not only due to its attack power, but the fact that Elephants and Circuses are closely intertwined. Elephants are known for being star attractions to any circus.
Michio is one of the few duelists mentioned to regularly defeat LDS Students. This may seem a bit of an informed ability at first, but when you look at the way his cookmate deck works, you realize it's an anti-meta deck, which is murder against the Fusion, Synchro and XYZ monsters LDS students use.
Michio's deck is very good at destroying monsters via card effect. This means that there is very little his opponent can do against him, while he then goes around and chips at their life points with burn damage and a bunch of little monsters. However, Yuya is actually a very bad matchup for him, because Pendulum monsters can keep coming back from the dead (as Yuya exploited).
Both of the mysterious duelists we have seen use Xyz monsters. They also appear to come from the ruins of Heartland City, a place known for its Xyz monsters.
Ritual Monsters are the first old 'summon forms' that appeared outside of LDS, and was known about by a non-Sora child character from You Show (Tatsuya). It's also the only of the 'summon that predates Pendulum Monsters that does not use the Extra Deck. While Ritual Monsters did have a cameo suggestion of being an LDS course in Episode 3, they aren't what LDS advertises because they are not a Extra Deck card type.
In episode 22, the narrative goes around showing and proving that Mieru's predictions are always right. Well, in episode 23, she was right for the wrong reasons about the upright Tower, saying that it represented very bad omens for Yuya and that his life could be at risk. Considering that a freaking chandellier practically fall over him, you can see she was right. But he manages to be ok from that and win. Well, the Tower also represents breaking free of old, unhealthy believes in order to think out of the box: Yuya literally screwed destiny and managed to break the mold of Pendulum summon to achieve victory.
In episode 23, following the Tarot Motifs, in the major arcana, after the Tower card (that in the episode, represented Yuya's uncertainty and defeat) comes the Star card (that represents hope). Well, in that episode he fuses his ace card, Odd-Eyes, with Stargazer Magician.
In Episode 24, Shun's deck makes sense for his mission. It seems to be tailored as anti-special summon (i.e. LDS's extra deck) weapon, which is why he was able to beat the LDS trio like that.
Like the Dark Duelist, Shun uses the word 'hangyaku' (rebellion) in his summon chant for his ace monster, and his attack name for it is 'Brave Claw Revolution', mirroring 'Revolt of the Lightning' for Dark Rebellion Xyz Dragon. Now remember that they're fighting Academia. The use of words like that is to symbolize them as the oppressed rising against an overwhelming enemy, hence Shun's Badass Boast to the LDS trio and his chant for Rise Falcon also mentioning 'from adversity'.
On top of that, Shun's Badass Boast perfectly sums up the duel, he's badly beaten and fighting on the edge (the LDS trio using their monsters to obliterate his field and hand, leaving him an instant from defeat), stands back up again (using Raid Raptors - Readiness to avoid losing the duel and Dimension Xyz to summon Rise Falcon), and overwhelms and eradicates his enemy (using Rise Falcon's effect to increase its ATK and attack all the opposing monsters at once).
Also, the name of the BGM which starts when Shun activates Readiness is A Duelist Cornered. This name perfectly sums up the position Shun was in, so why did it only start playing at the moment he escapes the pinch he's in? Because Shun isn't truly cornered. From what we see in the duel, his strategy lets his opponents think they have him cornered, before he reverses the situation entirely with Rise Falcon's overwhelming power.
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.
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.
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.
When your monsters have a tendency to tear up the surrounding location and send debris flying everywhere, it makes perfect sense to wear facial protection (especially as demonstrated in Episode 7), even disregarding the need (or lack thereof) to conceal identity. This begs the question of why Yuto didn't bother to obtain a new set.
His mask is military grade, maybe they don't sell such things in Japan.
He kept the mask, but ditched the goggles after they broke. Goggles should be readily available for protection, though, in various styles, too.
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.
On the other hand, the amount of real damage inflicted from such duels is variable. In 5Ds, it is stated that while Psychic Duels and Shadow Duels both can inflict real damage to the point of lethality, the latter is considerably more dangerous. Later on, Aki is able to control how much damage her psychic powers cause, so it's a fair assumption that Action Duels have toned down damage compared to a regular Psychic or Shadow Duel. The "worst" that would likely happen in an Action Duel is severe injury, such as broken bones, but death would probably very rare compared to the other Duel types.
However in Episode 23, the dangers of an Action Duel become mildly apparent. Mieru, Yuya's current opponent, repeatedly tells Yuya to forfeit due to a psychic reading stating that destruction awaits him if he continues on his path. When Yuya refuses, Mieru immediately turns up her dueling and tries to end the game as quickly as possible to avoid the fate thus worrying about the apparent danger that the Action Duel could cause. It turns out she was right as the Chandelier hanging above the stadium collapses right as Yuya goes after the Action Card. While Yuya ends up okay (come on, the theme of the episode was defying fate), it leaves one to wonder...why the hell the Chandelier collapsed like it did? We saw the chains weakening and breaking with very little stress on them (the duel didn't come anywhere near there). How did it happen?
Somewhat alleviated in episode 27. The younger kids' Action Duel fields are cushioned.
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?
Considering that The Dark Duelist/Yuto was surprised to see Shun, who was the guy who attacked Marco, this was probably just a coincidence.
Or, Fridge Squick: It is quite possible that Yuya has a fondness of softcore hippo pornography, if the opening is anything to go by, if not an outright fetish. Look at the skimpily-attired hippos. Now look at Yuya during the scene. You may vomit now; I'll certainly be...
You know those massive gouges Shun's monster makes in sheet metal? Makes it awfully convenient that the whirlwind it created when summoned blew everyone away. Getting your soul sealed into a card would be the least of your worries, then...
Also an In-Universe one, since Masumi is terrified when she sees them.
Let's not even get started on Yuto/ The Dark Duelist's hometown. It looks like the Satellite, but instead being the ruins of HEARTLAND CITY as oppose to Domino City, and its filled with gang warfare between duelists. What in the name of the Sacred Beasts happened since Zexal?