When playing a spell that gets countered by a reaction like Wind Wall, when do players pay the costs for their cards?

Ruling: Both players pay the energy and power costs when they declare and play their cards (as they enter the chain), not when the cards resolve. If your spell is countered by Wind Wall, you still pay the costs for your spell because you already paid them when you played it.

Sequence:

• Declare the spell you want to play
• Pay the energy and power costs for that spell as it enters the chain
• Opponent reacts with Wind Wall
• Opponent pays the energy and power costs for Wind Wall as it enters the chain
• Chain closes and resolves
• Both cards are trashed (your spell is countered, Wind Wall resolves)

Nuances:

• Some cards have additional costs stated in their card text (like Get Excited's discard or Bullet Time's power cost) that are paid at spell resolution, not when entering the chain
• For cards with resolution-time costs, if the spell is countered, those additional costs don't need to be paid
• A card is not considered 'played' until it has resolved, even though costs are paid when it enters the chain