Rhystic Study
Enchantment
Whenever an opponent casts a spell, you may draw a card unless that player pays 
.
"Despite her father's warnings, Valtry's fascination with the surface only grew. She collected things that fell to the bottom, daydreaming of life on land." —*The Merfolk Who Walked*
Illustrated by
Wilds of Eldraine: Enchanting Tales#25MythicEnglishLegality
Rulings
Oct 4, 2004
The player gets the option to pay when this triggered ability resolves. This will be after the spell is announced, but before it resolves.
Oct 4, 2004
You don’t have to decide whether or not you are drawing until after the player decides whether or not to pay.