"You know that secret? The one that wakes you up at night in a cold sweat? The one you think no one else in the world knows? Well, guess what."

Curiosity

Enchant creature
Whenever enchanted creature deals damage to an opponent, you may draw a card.

The List

"Valtry gasped. The strange new coral was not coral at all, but a fallen drywalker! But how did it get to the bottom of Loch Larent?"
—*The Merfolk Who Walked*

Wilds of Eldraine: Enchanting Tales

Li'l Giri tracked the robotic villain with silent steps. Just as the monster was about to eat the child . . .

Secret Lair Drop

"Surely you know the joy of the hunt, my furry friend. My kind of hunt just takes a different form than yours."

Jumpstart

All Mirri wanted to do was rest, but she couldn't ignore a nagging suspicion as she followed Crovax's skulking form.

"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 or to a battle.

If you control Curiosity and it's enchanting an opponent's creature, you won't draw a card when that creature deals damage to you. The creature has to deal damage to one of your opponents for the ability to trigger.

You draw one card each time the enchanted creature deals damage to an opponent, no matter how much damage it deals.