A Guide to Fire Kings

	Book of Eclipse Quick-Play Spell Change all face-up monsters on the field to face-down Defense Position. During the End Phase of this turn, change as many face-down Defense Position monsters your opponent controls as possible to face-up Defense Position, then your opponent draws cards equal to the number of monsters changed face-up by this effect.
	Book of Moon Quick-Play Spell Target 1 face-up monster on the field; change that target to face-down Defense Position.

Both of these are really versatile cards, if you think about it.

They can protect your monsters from effects that target, like Effect Veiler. It's the same trick we talked about when discussing Fire King High Avatar Kirin and Circle of the Fire Kings.

You can also use them as an interruption during your opponent's turn. With Eclipse, you'd ideally use it before pulling the trigger on Garunix Eternity, Hyang of the Fire Kings so he can wash away all the cards flipped face-down by this effect. (Keep in mind that your opponent can Set a monster face-down and it will count for this card's End Phase effect, getting them a draw. Not many people do this, though.)

Finally, they're good board breakers if you go second.

Depending on your personal preferences, you might prefer one over the other or neither at all.