Rhystic Study reads: "Whenever an opponent casts a spell, you may draw a card unless that player pays {1}." The trigger fires whenever an opponent casts a spell, but the draw effect is replaced by the opponent's option to pay {1}. If the opponent pays, you do not draw. If they decline to pay, you draw a card.
Under CR 603.1, triggered abilities trigger when their trigger event occurs and their conditions are met. The relevant condition here is structured as a 'may … unless' clause, meaning the opponent's payment directly prevents the draw effect from resolving in your favor. This is a cost the opponent can choose to pay as the spell resolves on the stack (CR 116.2b covers optional costs paid by players other than the active player).
It is important to note that the ability still triggers regardless — it goes on the stack every time an opponent casts a spell. The payment decision happens when the triggered ability resolves, not when it triggers. So your opponents must always acknowledge the trigger and decide whether to pay.
Concrete example: Your opponent casts Lightning Bolt. Rhystic Study's ability triggers and goes on the stack. When it resolves, your opponent says "I pay {1}." They add {1} to the mana pool and pay it — you do NOT draw a card. If instead they say "I don't pay," you draw one card.
This means opponents who consistently pay {1} for every spell can completely shut off Rhystic Study's card draw, though doing so costs them extra mana each time, which is still a meaningful tax effect (CR 119.1).
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.