Costs and Payments

No. Countering does not refund any costs paid to play a card, activate an ability, or trigger an ability, including additional costs.^{[425.1.c][425.1.c.1]}

A countered card or ability does nothing and is cleared from the chain,^[425.1.a] but anything already spent, discarded, killed, or otherwise paid as a cost remains paid.

Optional additional costs are additional costs a player may choose to pay.^[356.2.b.1]

Their rules text uses both "may" and the exact phrase "as an additional cost." Accelerate and Repeat are keyworded optional additional costs.^{[805.1.a][820.1.d]}

The player chooses whether to pay an optional additional cost while making relevant choices. If chosen, it is included while determining the card's total cost before applicable discounts are applied.^{[355.1.a][356.2][356.4]}

Additional costs and cost increases still apply. Playing a card "ignoring its cost" sets only its base energy and power costs to zero.^[356.1.b.1] Additional costs and cost increases are applied afterward and can raise its total cost above zero.^[356.1.b.3]

Mandatory additional costs must still be paid, while optional additional costs may still be chosen and paid.^{[356.2.a.1][356.2.b.1]} By contrast, "ignoring any and all costs" sets the card's total cost to zero, including non-standard costs.^[356.5.a]

Not through a normal reaction window. Costs are paid while the card or ability is being finalized, and finalization does not pass priority.^{[357][404][337.1.a]}

When resources are required, the player paying them may activate eligible Add abilities with Reaction during that payment.^{[429.3][444.2.c]} This is a special permission for resource payment, not a normal reaction window: those abilities finalize and resolve immediately without passing priority.^{[429.2][429.2.a]}

Any normal opportunity to react comes only after finalization, when the costs have already been paid.