Flip 1 face-up monster on the field into face-down Defense Position.
- * When you activate "Book of Moon" during the Battle Step to flip your defending monster into face-down Defense Position, the attack resolves as normal. No replay occurs because the possible attack targets on your side of the field did not change. 
* When you activate "Book of Moon" during the "Battle Step" to flip an attacking monster into face-down Defense Position, the attack stops. No replay is triggered. The attacking monster cannot change its battle position in "Main Phase 2", because it is still considered to have declared an attack. (So it cannot be Flip Summoned in "Main Phase 2".) 
* If you are attacking, and you chain "Book of Moon" to your opponent’s "Mirror Force" to flip one of your monsters face-down, that monster is not destroyed by "Mirror Force". 
* If you chain "Book of Moon" to "Magic Cylinder", "Ring of Destruction", or "Trap Hole" to flip the target of any of those cards face-down, the card’s effect disappears. (See "Activation & Targeting Eligibility" in the Advanced FAQ.) 
* If you chain "Book of Moon" to "Bottomless Trap Hole", the now face-down monster will not be destroyed by "Bottomless Trap Hole", but any other appropriate monsters Summoned at the same time will still be destroyed.
* If you use "Book of Moon" on "Dream Clown", "Dream Clown"’s effect is not activated.
* If you chain "Book of Moon" to the activation of a Flip Effect Monster’s effect, such as "Fiber Jar", "Book of Moon" flips the monster face-down again, but the Flip Effect still resolves as normal.
* You cannot flip a Monster Token face-down because Monster Token are always face-up.
* You cannot activate "Book of Moon" while "Light of Intervention" is active.
"Book of Moon" is one of the most versatile Quick-Play Spell Cards in the game. It has several very useful applications.
o You can use it to flip an opponent's monster face-down in the Battle Step. Since that has officially declared an attack, your opponent cannot then Flip Summon that card in Main Phase 2.
o You can use it to flip one of your monsters face-down in the Battle Step. This can be especially useful for cards such as Old Vindictive Magician, Marshmallon, or any other cards with Flip Effects, or other effects that are beneficial when flipped face-up.
o In your Main Phase, you can flip one of your opponent's monsters face-down, as a preliminary measure before using Nobleman of Crossout, Dark World Lightning, Shield Crush, or cards that destroy defense monsters to destroy that monster.
o You can chain Book of Moon to the activation of Light and Darkness Dragon to renew its ATK and DEF
o You can save your monster from being affected by opponent's cards; you can chain this card to Sakuretsu Armor, Mirror Force, Lightning Vortex or Magic Cylinder.
o If you use destruction effects, you can use this first to counter the effects of Stardust Dragon as well as its more advanced forms. Since your opponent can't use the effect of a face down monster, you're in the clear.
o Provided the monster hasn't changed its battle position this turn, you can activate an Ignition Effect that can only be used once per turn, use this card on that monster, and then Flip Summon said monster to use its effect once again.
o This card resets almost any (if not all) lingering effects affecting a monster (including Gemini summon status). So if it was Special Summoned by Call of the Haunted, the Trap Card doesn't affect your monster anymore, or if it was a Synchro Monster Special Summoned by Eccentric Boy, then Eccentric Boy's effect is no more applied and so on.
* You can use this card with Red Dragon Archfiend if your opponent prevents you from attacking to save your monsters from destruction or to destroy a monster they have.
* This card can be used if an Arcana Force monster you summon gains its negative effect.
* Because face-down monsters can't be used as synchro material, this card is ideal for stopping a synchro summon.
Gracias a su versatilidad una carta sin duda alguna para profesionales y uds que piensan?