Curiosity | Magic: The Gathering
Formats Curiosity is Legal in
Official Oracle Text for Curiosity
Whenever enchanted creature deals damage to an opponent, you may draw a card.
Official Rulings for Curiosity
2/1/2007 : If put on your opponent's creature, you do not draw a card when that creature damages you. The creature has to damage your opponent in order to have this work.
2/1/2007 : Drawing a card is optional. If you forget, you can't go back later and do it, even if it is something you normally do.
9/22/2011 : "You" refers to the controller of Curiosity, which may be different from the controller of the enchanted creature."An opponent" refers to an opponent of Curiosity's controller.
9/22/2011 : Any damage dealt by the enchanted creature to an opponent will cause Curiosity to trigger, not just combat damage.
9/22/2011 : Curiosity doesn't trigger if the enchanted creature deals damage to a planeswalker controlled by an opponent.