If any of the chosen creatures require paying costs to attack, or if any optional costs to attack were chosen, the active player determines the total cost to attack. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. Once the total cost is determined, it becomes “locked in.” If effects would change the total cost after this time, ignore this change.
January 25, 2019 · Ravnica Allegiance
If any of the chosen creatures require paying costs to attack, or if any optional costs to attack were chosen, the active player determines the total cost to attack. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. Once the total cost is determined, it becomes "locked in." If effects would change the total cost after this time, ignore this change.
April 28, 2017 · Amonkhet
If any of the chosen creatures require paying costs to attack, or if any optional costs to attack were chosen, the active player determines the total cost to attack. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. Once the total cost is determined, it becomes “locked in.” If effects would change the total cost after this time, ignore this change.
May 1, 2014 · Journey into Nyx
If any of the costs require mana, the active player then has a chance to activate mana abilities (see rule 605, “Mana Abilities”).
September 30, 2011 · Innistrad
If any of the costs require mana, the active player then has a chance to activate mana abilities (see rule 605, "Mana Abilities").
June 17, 2011 · Commander 2011
If any of the costs require mana, the active player then has a chance to activate mana
April 1, 2011 · Duel Decks: Knights vs. Dragons
If any of the costs require mana, the active player then has a chance to activate mana abilities (see rule 605, "Mana Abilities").
February 4, 2011 · Mirrodin Besieged
If any of the costs require mana, the active player then has a chance to activate mana abilities (see rule 605, “Mana Abilities”).
October 1, 2010 · Scars of Mirrodin
If any of the costs require mana, the active player then has a chance to activate mana
February 1, 2010 · Worldwake
If any of the costs require mana, the active player then has a chance to activate mana abilities (see rule 605, "Mana Abilities").