Swords of Concealing Light
In the recent Yu-Gi-Oh! World Championship 2016, during the first feature match, a ruling issue came up when Samir Bachar played Swords of Concealing Light and Hiyama Shunsuke responded with the effect of his Dragon Spirit of White.
When the Chain resolved, Blue-Eyes White Dragon was special summoned, and then Number 95: Galaxy-Eyes Dark Matter Dragon was flipped face-down. The newly special summoned Blue-Eyes White Dragon remained face-up.
Official OCG Ruling
The official Yu-Gi-Oh! Card Database was updated yesterday, and the new Q&A for Swords of Concealing Light reaffirmed that the ruling at the World Championship 2016 was the correct way that Swords of Concealing Light was meant to function.
Will the monster special summoned by the effect of “Call of the Haunted” that was chained to the activation of “Swords of Concealing Light” be in face-down Defense Position?
In this scenario, I activate “Swords of Concealing Light”.
If the opponent chains and activates “Call of the Haunted” in response to that activation, and special summons “Dragon Spirit of White” from the graveyard, which monsters will be in face-down Defense Position?
The monsters that will be changed to face-down Defense Position by the effect “When this card is activated, all monsters on the opponent’s field becomes face-down Defense Position” of “Swords of Concealing Light”, are only those monsters that were face-up in the opponent’s Monster Zone at the time of activation.
Therefore, in the scenario of the question, “Blue-Eyes White Dragon” will be in face-down Defense Position, “Dragon Spirit of White” which was not in the opponent’s Monster Zone during the activation of “Swords of Concealing Light” will not be in face-down Defense Position.
2016-08-25
Swords of Concealing Light
This meant that Swords of Concealing Light is very much ineffective against special summons that could be chained to its activation.
Blue-Eyes Spirit Dragon and Dragon Spirit of White could be activated in response to Swords of Concealing Light. The Dragon-Type monster special summoned will remained face-up and thus could be protected by the graveyard effect of Return of the Dragon Lords.
Mask Change could be chained to Swords of Concealing Light, and Masked HERO Dark Law would be special summoned and remained face-up.
Book of Eclipse
Comparatively, Book of Eclipse is much more effective for disabling Quick Effects that special summons.
However, Book of Eclipse requires an immediate follow-up in the same turn.
Swords of Concealing Light could buy you up to 2 turns if the opponent does not have any Spell card removal effect to take out Swords of Concealing Light.
Conclusion
With both pros and cons to Swords of Concealing Light and Book of Eclipse, a good read and understanding of the popular decks is necessary to pick the right card for the metagame.
While Swords of Concealing Light was the more popular choice, Book of Eclipse has been experiencing a spike in recent days.
Update on 2017-02-25: This ruling has since been reversed (see Swords of Concealing Light Ruling Reversal).
Wrong. This was a major rules overlook from Konami side.
As of 2024 rules Swords of Concealing will flip every monster currently on the opponent field to facedown position on resolve, regardless if they weren’t present during the card activation. This is how the card resolves and was programmed to work in every digital version of the game. Including Master Duel.
This was a very powerful card before Links monsters coming into existence.