You can’t activate “D.D. Designator” if you have no cards in your hand, or if “D.D. Designator” is the only card in your hand.
If you have your opponent’s card in your hand because of “Exchange”, you can remove it from play if you name a card your opponent doesn’t have in his hand.
You declare the card name when you activate “D.D. Designator”.
If your opponent has no cards in his hand when “D.D. Designator” resolves, the effect of “D. D. Designator” is negated.
You can’t activate “D.D. Designator” when your opponent has no cards in his hand.
If you activate “D.D. Designator” and your opponent has 2 copies of the same card in hand, you (the player who activated “D.D. Designator”) select which of the 2 cards is removed from play (this can be important if your opponent holds your card because of “Exchange”).
Netrep Rulings:
You MUST have another card in your hand besides “D.D. Designator” in order to activate this card.
If you no longer have an additional card in your hand when “D.D. Designator” resolves (for example, if you activate “Type Zero Magic Crusher’s” effect in a chain), then “D.D. Designator’s” effect disappears.
If “Reload” is chained to the activation of “D.D. Designator,” “Reload” must resolve first before the hand is revealed for the effect of “D.D. Designator.”