Souvick Kar's Top 32 Evilswarm deck used both Dark Armed Dragon and Black Luster Soldier - Envoy of the Beginning; Compulsory Evacuation Device was missing from a big portion of the lists altogether; Closed Forest saw play in a few Side Decks; and several other little things were going on that made that Top 32 kind of revolutionary. The biggest tech pick for me was Stephen Mercier's decision to Side Deck two copies of the long-time-junk-box-filler Swords of Concealing Light.Conceal, Don't Feel
For all the negatives of Swords of Concealing Light, there are plenty of positives. The effect that turns all of your opponent's monsters face-down doesn't target, so the list of cards that stop it is extremely limited. Things like Safe Zone, Bujingi Turtle and Noble Arms - Excaliburn can't prevent it from ruining fields, and the lack of any destruction effect circumvents Musakani Magatama, Stardust Dragon, Bujingi Hare and those types of effects. Short of those cards that would destroy Concealing Light before it resolves, you can be guaranteed monsters are getting set.
After that, your opponent can't change any of their monsters' battle positions, including those that get Summoned post-resolution. Enemy Controller and Book of Moon are both stronger during that window before Concealing Light pops itself, though Enemy Controller's decline in popularity makes it less of a factor. In the same way, anything that limits or interferes with the subsequent Summons your opponent tries to make is way more effective while Concealing Light's on the field. Compulsory, Bottomless Trap Hole and Solemn Warning all become turn-ending cards, and Torrential Tribute is way scarier since you have to commit another monster to an already-populated field.
Pairing Swords with Kaiser Colosseum's a strong combo for the same reason. If you disable all of your opponent's monsters for two turns and prevent them from Summoning as long as they have any of them left on the field, there isn't much they can do to push against you. That gives you time to set up a field or pick off the monsters you don't want to deal with before they can go face-up again. Stephen Mercier used that strategy at YCS Atlanta and took a commanding Top 16 finish, proving it effective. Two turns is a surprisingly long time to watch Bujintei Susanowo and Bujintei Kagutsuchi come out and brutalize your everything.
There are some convoluted ways to skip Concealing Light's self-destruction, like using Solomon's Lawbook to skip that Standby Phase, but they're way too gimmicky. That doesn't mean there isn't a good way to keep it around longer than it's supposed to be; Blackwing - Zephyros the Elite and Mist Valley Falcon can return it to your hand, giving you two more turns every time you re-activate it without costing you anything. Zephyros even gives you a 1600 ATK body to beat down one of the monsters you put in defense. You get a +1 of card economy for returning Zephyros to the field, and a +1 in battle or a wasted backrow; you come out ahead either way.
Everything else aside, it's mostly important to look at what makes Concealing Light better than other cards that counter the same decks. Noble Knights and Bujin are the two strategies it hobble sthe most, and they have a lot of counters anyway. Macro Cosmos, Mind Crush, Mistake, Light-Imprisoning Mirror and DNA Surgery all come to mind, but there are more. In spite of the problems a Continuous Spell usually faces, Concealing Light actually has an advantage as well. You can activate it, make monsters vulnerable and then strike at them during the battle phase of the same turn, playing aggressively instead of reactively. Past that, most of those cards suffer from the same weakness to Mystical Space Typhoon as Concealing Light, and become -1s as soon as you activate them. They do stay on the field and remain active, but they're not live options anymore than you can do anything proactive with.
Mistake suffers a timing problem, needing to flip before Yamato's gone off a couple of times or the Noble Arms find their way to the yard. If you draw it too late, it's useless. Flip it too far into the game and you risk losing it to an established Bujingi Quilin or your opponent already having done all of their necessary searching. Macro Cosmos doesn't help against Bujingi that are already in the graveyard, and it falls to Quilin the same way Mistake would. It handles Noble Knights a little better since the equips get banished, but you need Macro and something else to kill the Noble Knight carrying those equips in the first place. Comparatively, Concealing Light works at any time there are monsters up, regardless of fields, hands or graveyards. It rips away Noble Arms, can't be destroyed with Quilin until it's already too late for the Bujin duelist, and it generally stays useful throughout the course of the game.Can't Hold It Back Anymore
Decks like Bujin that run Kaiser Colosseum have a distinct synergy with Concealing Light, and we've already seen competitive success to back up that theory. Locking down the field so efficiently while already answering the Battle Phase at the same time is incredible, but the Bujin preventing targeting and destruction is too much. Last week I talked about how Bujin could be built a few different ways, both with and without defensive trap lines (link for anyone who missed it), and Swords works equally in either. Bujin have a terrible time in the mirror match, since they can counter each other so explicitly: Turtle stops Quilin; Bujingi Crane versus Bujingi Crane's a stalemate 2-for-2; and both duelists have Bujingi Hare on standby. Concealing Light handles those mirror match problems by answering everything directly. Hare, Crane and Turtle all fail to protect Yamato and the other Bujins while they're face-down, and a lack of targeting means they'll go face-down every time. Bujintei Kagutsuchi can still protect itself if you try to attack it afterward, but that's about their only saving grace.
It's also exceptionally strong against Noble Knights, because nothing they have prevents Concealing Light from flipping down monsters. Since it hits all of them, your opponent won't even have any Noble Knights left to re-equip their Noble Arms to – no matter what happens to their monsters, you automatically get a +1 for each Noble Arms that gets detached. In most cases that'll be two to four, since Noble Knight Borz can search them out. Even assuming you had to use Swords of Concealing Light on a single Noble Knight with a single Noble Arms, which is stupidly conservative, if you run over that Noble Knight while it's face-down that turn, you've scored a +2 from Swords already. And there's no way they only have a single Noble Knight with a single equip unless you're already dominating the game anyway.
A Traptrix deck with three Mist Valley Falcon like the one TCGPlayer's own Bobby Kenny made Top 8 with last format, is good at exploiting Concealing Light in those match-ups. That deck's success was based on tech choices that countered the expected metagame concisely and efficiently, and a metagame with an abundance of Bujin or Noble Knights could see Traptrix become a valid anti-meta choice. Falcon recycling Swords of Concealoing Light until it dies in battle, then Beetron using Swords to get back Traptrix Myrmeleo before it destroys itself sounds absurd in all the right ways. Any deck that has the potential to counter others so directly should at least be considered, even if they're underpowered or underrepresented right now.Never Going Back
You'd have a hard sell convincing me that Swords won't become popular on a much more broad scale some time soon, considering it's had a YCS top and the deck list it was played in has attracted considerable attention. It'd be reasonable to expect the secondary market to reflect that soon if it doesn't already. Against Bujin, Noble Knights and most general king-of-the-hill decks, it's too strong, and future Regional Top 8 lists are probably going to reflect that. People can't just turn away and slam the door on it anymore.