For a time the last ability triggered when Duplicity left the battlefield. It has been restored to triggering when you lose control of Duplicity.
2008-04-01
Taking control of another player’s Duplicity will trigger the ability that causes the cards they exiled to be put into their owner’s graveyard.
2004-10-04
The cards are face down all the time. You can’t look at them. This applies even to cards from your hand that got swapped out. You have to remember what they were if you care.
When this enchantment enters, exile the top five cards of your library face down.
At the beginning of your upkeep, you may exile all cards from your hand face down. If you do, put all other cards you own exiled with this enchantment into your hand.
At the beginning of your end step, discard a card.
When you lose control of this enchantment, put all cards exiled with this enchantment into their owner's graveyard.
