Convoke

• 502.46. Convoke
  • 502.46a Convoke is a static ability that functions while the spell is on the stack. “Convoke” means “As an additional cost to play this spell, you may tap any number of untapped creatures you control. Each creature tapped this way reduces the cost to play this spell by or by one mana of any of that creature’s colors.” Using the convoke ability follows the rules for paying additional costs in rules 409.1b and 409.1f–h.
    • Example
      You play Guardian of Vitu-Ghazi, a spell with convoke that costs . You announce that you’re going to tap a colorless creature, a red creature, and a green-and-white creature to help pay for it. The colorless creature and the red creature each reduce the spell’s cost by . You choose whether the green-white creature reduces the spell’s cost by , , or . Then the creatures become tapped as you pay Guardian of Vitu-Ghazi’s cost.
  • 502.46b Multiple instances of convoke on the same spell are redundant.

(409. Playing Spells and Activated Abilities)

• 409.1. Playing a spell or activated ability follows the steps listed below, in order. If, at any point during the playing of a spell or ability, a player is unable to comply with any of the steps listed below, the spell was played illegally; the game returns to the moment before that spell or ability was played (see rule 422, “Handling Illegal Actions”). Announcements and payments can’t be altered after they’ve been made.
  • 409.1b If the spell or ability is modal (uses the phrase “Choose one —” or “[specified player] chooses one —”), the player announces the mode choice. If the player wishes to splice any cards onto the spell, he or she reveals those cards in his or her hand. If the spell or ability has a variable mana cost (indicated by {X}) or some other variable cost, the player announces the value of that variable at this time. If the spell or ability has alternative, additional, or other special costs (such as buyback, kicker, or convoke costs), the player announces his or her intentions to pay any or all of those costs (see rule 409.1f). You can’t apply two alternative methods of playing or two alternative costs to a single spell or ability. Previously made choices (such as choosing to play a spell with flashback from his or her graveyard or choosing to play a creature with morph face down) may restrict the player’s options when making these choices.
  • 409.1f The player determines the total cost of the spell or ability. Usually this is just the mana cost (for spells) or activation cost (for abilities). Some cards list additional or alternative costs in their text, and some effects may increase or reduce the cost to pay. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. The total cost is the mana cost, activation cost, or alternative cost, plus all cost increases and minus all cost reductions. Once the total cost is determined, it becomes “locked in.” If effects would change the total cost after this time, they have no effect.
  • 409.1g If the total cost includes a mana payment, the player then has a chance to play mana abilities (see rule 411, “Playing Mana Abilities”). Mana abilities must be played before costs are paid.
  • 409.1h The player pays the total cost in any order. Partial payments are not allowed.
    • Example
      You play Death Bomb, which costs and has an additional cost of sacrificing a creature. You sacrifice Thunderscape Familiar, whose effect makes your black spells cost less to play. Because a spell’s total cost is “locked in” before payments are actually made, you pay , not , even though you’re sacrificing the Familiar.