Ultra Rares
Slate Warrior: Starting off simple, this is a 1900 beater that has the potential to become 2400 if left set for a turn. Sadly, no one leaves set cards sitting when most of the meta punishes set monsters with cards like Dakini, Gladiator Beasts, and Hydrogeddon. I don't see any competitive merit here.
Salvage: An interesting choice. This card was primarily used in the physical card game as a combo extender with Atlantean Mermails, Frogs, and even Gishki. However, this box doesn't include the key Gishki cards that abused this, and Duel Links doesn't have the other archetypes in complete forms. I don't see much use, but they did include some cards to try and combo with it.
Abyss Soldier: Now we see one of the reasons why Salvage was included. This card is actually quite powerful, considering the impact that Snipe Hunter had. Bouncing to hand isn't as good as popping, but this isn't a gamble and it doesn't matter if the card goes back to their hand if you end them in one turn. Definitely keep an eye on this one, as if any water deck shapes up to be tier this will find a home there.
Ties of the Brethren: Wow. This card is full of potential. It's flexibility and use with any coherent set of monsters means that you're only limited by your imagination (and the hefty LP cost and restrictions.) I could see any number of things working out. From consistently loading up with Magnets, to getting to Bountiful Artemis consistently, to fielding your full set of fiends for Dark Necrofear, I highly look forward to seeing what people can do with this. Still, I can't help but fear that the presence of burn will make this a non-factor.
Gishki Chain: This card has no potential; rather, it will definitely be immediately competitive. Cyber Angels already were a force in the meta, and this is on par with each of the already-powerful searchers included in current variants. I can see Balance CA decks dropping Senju and Petite to a single copy each to merely be search targets and including 3 of this card instead. Not to mention the revitalization it gives to other off-meta ritual decks like Relinquished. This card alone could make this box be worth going through 3 times for the P2W player.
Mystic Piper: Speaking of Relinquished, a cute card that is very near and dear to me personally. This is one of my favorite cards in the physical card game, and I'm disappointed that it doesn't seem to have a home in Duel Links. The pace of the game is prohibitive to spending a normal summon and a card to draw one and sometimes two cards. If it weren't ultra, I definitely would want to make some sort of Relinquished Mystic Piper deck work though, just for fun.
Evigishki Levianima: The first of one of the big water archetypes encountered in the abyss of this box, Gishkis. It has a draw effect on attack that lets you look at your opponent's hand if successful, but the real use is the +1. However, Cyber Angel Dakini gets card from grave as a +1, but can do it first turn and without having to attack into backrow, not to mention her send to grave removal effect. If Gishki have a place in the meta, this might warrant inclusion, but it will probably just be the inferior ritual deck, banlist pending.
Archfiend Emperor, the First Lord of Horror: The first of the other big, more evil archetype encountered in the abyss, Archfiends. This card is scary. In the physical card game, normal summoning a 1500 beatstick that could pop a card then die wasn't scary. In Duel Links, it is, and the threat of it coming back twice as big with a lot more destruction waiting in the wings is formidable. The "can only special summon fiends" restriction is a non-factor when this card is best placed in a Necrofear-based deck with other Archfiend and fiend support as well, and I see some sort of fiend deck being a solid tier 2-3 contender. Maybe even with That Grass Looks Greener.
The Legendary Fisherman II: Mako gets some love with this retrain of his original and vastly inferior fisherman. With support from The Legendary Ocean this card is powerful, protected, and easily summoned. And when it's taken down, it replaces itself with another very important monster I'll cover later. This card is scary, and while I shy away from inherent inconsistencies of a level 5 tribute monster, I would say a deck focused around it and the card it searches will be a shoo-in for tier 2 or even tier 1.
Water Dragon Cluster: Bastion also gets some love with some more chemistry-themed big bad wet dragons. It has an incredibly powerful on-summon effect that reveals the strongest boards as paper tigers that can be just waltzed for an OTK. However, you can't use either of it's effects unless you can successfully summon it in the first place, and while it did get a reusable support spell and powerful trap, it's a massive and inconsistent investment to summon. While there's plenty of fun to be had with Diamond Dude meme decks, I think the only real home for Hydrogeddon will be in Dinos.
Super Rares
Skull Archfiend of Lightning: It's a Summoned Skull retrain that fits with the card being an Archfiend card despite some naming issues. Summoned Skull is old enough that name stamp archetypes weren't a thing they were expecting to have to localize for, so both it and this retrain work with all the Archfiend support in this box. This one is barely better than the original though, with a 50/50 shot of negating a card that targets it, but nothing proactive and LP payments in the standby phase. It's bad.
Warrior of Atlantis: Remember how The Legendary Fisherman II was terrifying but possibly too inconsistent? This card changes that, giving you potentially 6 copies of A Legendary Ocean to easily summon your fisherman while being a respectable beater in it's own right. There's definitely something here to make some sort of good deck.
Mysterious Triangle: The first Alien card. It is an extremely powerful +1 than has strict activation conditions and a drawback of losing your monster in the end phase. However, most A-Counter generators are terribly inconsistent and slow. All but one, that I'll be going over later. This deck will be dependent on that lone card, and this card's use will depend on one thing: if that card can carry the deck.
Power Breaker: A curious card to say the least. It's reminiscent of Spear Dragon but with a different bonus that might be more relevant. However, the most important face-up S/T cards you'll want to remove are Burn's defensive cards, and in that matchup this card will just die to Lava Golem. I don't think it has a place in the meta.
Axe of Fools: Another equip spell with minimal competitive merit. Mask of the Accursed is probably better for Burn, and while Axe of Fools does bring your Archfiend Emperor to 4000 attack, it still dies during the end phase. Attack-boosting equip spells are just inherently inconsistent and rarely worth it.
Evigishki Mind Augus: Another Gishki ritual boss. This one is neat, because it has no restrictions on what it can return to the deck. This means that a dedicated Gishki deck can prevent themselves from decking out by looping two of these. Having another deck like Gladiator Beasts that can potentially go infinite means we are one step closer to Mill being unviable as a strategy, which I'll never complain about. Even in non-Mill matchups it allows for you to force your opponent to act as the aggressor lest they lose to deckout, which is useful and can net you wins when your opponent has to play into your backrow.
Gishki Aquamirror: If none of the other Gishki cards were very good, this one is. Where Benten allows CA to ritual summon while keeping their hand full, this card allows Gishki to ritual summon while keeping their hand full, and you'll never run into the issue of only having so many ritual summons in your deck before you're out. That's a problem that CA decks used to have, with only 4 ritual spells and otherwise needing to recycle MAR with Dakini. Gishkis might not be there just yet, but they do have very solid tools. The question remains whether it will be better to just run CA, or if CA will be hit yet again.
Archfiend Cavalry: An incredibly solid Archfiend core card, in my opinion. A respectable beater with the Archfiend name and fiend type who floats, it also has a specific synergy with an Archfiend trap I'll be going over later. This card will definitely be mandatory in any Archfiend deck going into the future.
Citadel Whale: This card is the search target for The Legendary Fisherman II, and it pulls it's weight. Special summonable from hand or graveyard, it fetches the trap I'll cover next while also having it's own built in protection-from-targeting effect. I'm predicting it'll be a powerhouse once the box is out.
Sea Stealth Attack: Citadel Whale's partner-in-crime. It lets you reuse a fallen A Legendary Ocean which is nice, but the real power is the other effects. You can banish a water monster until the End Phase to protect your face-up S/Ts, which useful as a dodge effect to avoid monster destruction as well as protection for your S/Ts, and it's a continuous Super Rush Headlong for your big water monsters. This means that a summoned Citadel Whale can protect itself from targeting and destroys any monster that it battles before damage calculation while also being able to dodge until the end phase. That is a terrifying set-up to try and break through, and I fear it will be too powerful and meta-warping. Even if The Legendary Fisherman II doesn't find a place, Citadel Whale Turbo could just be tier 1 on its own.
Duoterion: One of the other pieces of Bastion support, this card tries to be the glue that binds the bonding deck together. However, I don't think it succeeds. While it can search two powerful new support cards, being level 5 means that it's not very useful on it's own outside of that role. It's own on-summon effect merely gets back the monster you tributed for it, which isn't even plus. I expect there might be a fun Water Dragon meme deck that just includes all the Water Dragon and Bonding cards that wins when it opens exactly 2 Duoterion, 1 Oxygeddon, and Bonding - D2O (or the third Duoterion,) but it won't be competitive. On the plus side, the trap lets you shuffle from grave so it's not as minus. It's just glacially slow and predictable.
Call of the Archfiend: This card is a lot more competitive, in my opinion. Once your Archfiend Emperor is in grave, this lets you get him back at full power while putting a fiend in grave for fuel for his effect. It is everything that the Necrofear fiend mashup decks needed to be competitive. The problem always was even if you could search your big bosses with Doomdog Octhros, they were too hard and/or too slow to summon. Now, not only is Archfiend Emperor the new best Doomdog target for that kind of deck, this card actually gives you a good way to field it and other almost-viable big bosses like Archfiend Empress as well, and you can use it multiple times as long as you have the fodder in hand.. I can't wait to see if a That Grass Looks Greener fiend deck using this springs to the forefront.
Rares
There's a lot of them, so I'll be going over them in groups that stand out and will pass over most of the chaff. It's definitely possible that I miss one that's good though, so be sure to let me know in the comments what you think.
Archfiends: There's a lot of random die roll archfiends that make you pay life, and a field spell. The field spell has a good effect but might not be worth the deck space. I think the most important cards will be the 1900 vanilla and Archfiend's Roar. Archfiend Soldier is the next best normal summon past Archfiend Cavalry, and more cheap 1900 beatsticks is good for auto duels and budget players alike. Archfiend's Roar is better than Call of the Archfiend. There's no discard cost, but it goes to grave as fodder for Archfiend Emperor anyways. While the monster summoned dies in the end phase, you can revive Cavalry who revives something else so it can still be a permanent Archfiend Emperor. There's a lot to work with here.
Aliens: The bulk of Alien cards are down here, so this will be a pretty budget archetype. There are a variety of useful effects. Alien Telepath can pop S/Ts, and both Alien Hypno and Brainwashing Beam can steal monsters. There's some slow and meh A-Counter generators, and then there's "A" Cell Recombination Device. This is the best Alien card, hands down. Instant, fast, loads of counters, and it fetches you an Alien to use the counters with. If Aliens are a deck, it will be on the back of this card. I'm happy to say that it's cheap and seems strong enough that I at least will be giving it a try.
Gishki: There are two other Gishki boss monsters here, and both are fine. Attacking the opponent's hand is good, and the other boss has a nice statline. Sadly, none of the non-rituals are particularly stellar. Gishki Beast is plus but can't be used very well except as ritual fodder. The best Gishki monsters were in the D.D. Water tower or the holos of this set, it seems. However, Forbidden Arts of the Gishki can be strong as removal and probably warrants a spot.
Miscellaneous: Mistaken Arrest, Damage Diet, and Showdown of the Secret Sense Scroll Techniques are all side deck material. For those who participate in tournaments with side decks, there's potential. Mistaken Arrest versus CA seems strongest in my opinion. Hundred-Footed Horror and Forbidden Chalice could be a fun meme, and Fishborg Planter works well in a water mashup deck. Two rare 1900 beaters are good as well, and I expect that the AI decks will need updating soon. Even the highest level AI deck based around level 4 vanilla beaters uses 1700 attack monsters still.
Commons
Less of note than even the rare section. I won't be dividing this by archetype because there's not much here. All of the Archfiend cards support Terrorking Archfiend even though Archfiend Emperor is far superior. All of the Alien cards are slow ways to load A-Counters that are inferior to "A" Cell Recombination Device or tribute bosses who don't do enough. I could see players maybe using Alien Mother, though, as she does have a good effect and lets you add 6 counters off Recombination, but Alien Overlord is more easily summoned. The spells and traps just aren't as impactful as the higher rarity good stuff. Gishki suffer from the same. They are all either not plus, too slow, or both. Gishki Photomirror is nice if costly, but Aquamirror is already so good and reusable.
However, there are two standouts. First, Golden Flying Fish is simply an excellent card for fish and water decks and has great synergy with the Ranked Duel reward Oyster Meister. Second, the previously-mentioned Bonding - DHO. The deck itself is lacking, but this card is powerful enough to enable some sort of meme deck, and the graveyard synergy has me interested in a That Grass Looks Greener build.
Closing Thoughts
This box is certainly an interesting one. It doesn't seem to have any obvious staple cards, but introduces support to make two powerful decks. I believe that Archfiend fiends and Citadel Whale water will have some place in the meta after this box. Aliens might be rogue, and there are plenty of fun meme decks to play with, too. Overall, while it's impossible to know for sure, I believe that at least 2 decks from this box will be competitors on par with the top decks from the KC Cup, and if there's another banlist or balance adjustment, they might be even stronger. However, as a F2P player, unless your heart is set on one of the archetypes from this box, you don't have to worry about missing out on anything that will be vital for a long time to come. Thank you for reading, and I hope you found this interesting and informative.