When do you choose to repeat a card - on activation or on resolution?

Ruling: You must choose to repeat when you pay the cost of playing the spell, as part of finalizing the card. The repeated spell creates one chain item with its effect twice, not two separate activations.

Sequence:

• Play the spell with Repeat
• Decide right then whether to pay the Repeat cost
• If paying Repeat, finalize the effect twice as one chain item
• Opponent then gets priority to respond

Nuances:

• There is only one activation, not two separate ones
• If the repeated spell is countered, you do not get the Repeat cost refunded (like any other additional cost)
• The Repeat additional cost is not factored into base cost thresholds for effects like Defy