Discarding a Spell Card is a cost. The effect of this monster targets a face-up monster that is removed from play. If “D.D.M. – Different Dimension Master” is flipped face-down or removed from the field, its effect resets and you can use it again that same turn if you can get him face-up on the field again.
If the opponent chains “Book of Moon” to his effect and flips “D.D.M. – Different Dimension Master” face-down, you still resolve his effect.
You cannot Special Summon a monster that was removed from play face-down using “Lightforce Sword” or “Different Dimension Capsule”.
“D.D.M. – Different Dimension Master” can Special Summon monsters in the “removed zone” of its controller. If your opponent controls your monster because of “Creature Swap” and it is removed from play, you can Special Summon it with “D.D.M. – Different Dimension Master” because it is in your removed zone. When the effect of “D.D.M. – Different Dimension Master” is used, the target monster is Special Summoned to the field of the player who controls “D.D.M. – Different Dimension Master”.