If the opponent approves Bullet Time and I then pay the cost, can the opponent use a reaction card?
No, the opponent cannot use a reaction card after you have paid the power cost for Bullet Time.
According to the official ruling for Bullet Time (referenced in the provided context from RiftJudge FAQs #5653 and #9105):
The Sequence of Events
- Cast: You pay the 1 energy cost and place Bullet Time on the chain.
- Reaction Window: Your opponent receives priority and may play reactions while Bullet Time is on the chain. They must make these decisions without knowing how much power you intend to pay.
- Resolution: After all reactions on the chain have resolved, Bullet Time begins to resolve. At this point, you choose how much power to pay and deal that much damage.
Why they cannot react after you pay:
- Payment happens during resolution: Paying the power is an action performed during the resolution of the spell, not as an additional cost during casting.
- No reaction window exists: There is no reaction window after the power amount is determined and paid during resolution. Once you begin paying the power, the damage is dealt immediately, and the spell is cleared from the chain.
In short, your opponent must decide whether to use a reaction card while the spell is still on the chain waiting to resolve. Once you move into the resolution phase and start paying the power, it is too late for them to react.