Curiosity

R3.63

“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.
Any damage dealt by the enchanted creature to an opponent will cause Curiosity to trigger, not just combat damage.
Curiosity doesn’t trigger if the enchanted creature deals damage to a planeswalker controlled by an opponent.
You draw one card each time the enchanted creature deals damage to an opponent, no matter how much damage it deals or whether it was dealt in combat.
If this Aura enchants an opponent’s creature, you won’t draw a card when that creature damages you. The creature has to deal damage to one of your opponents for the ability to trigger.”