Kicker

Kicker is a keyword ability that allows the player to pay an optional cost when playing a spell to achieve an additional effect.

All tournament-legal cards with kicker were printed during Invasion block.

From the Comprehensive Rules:

• 502.21. Kicker

• 502.21a Kicker is a static ability that functions while the spell is on the stack. “Kicker [cost]” means “You may pay an additional [cost] as you play this spell.” The phrase “Kicker [cost 1] and/or [cost 2]” means the same thing as “Kicker [cost 1], kicker [cost 2].” Paying a spell’s kicker cost(s) follows the rules for paying additional costs in rules 409.1b and 409.1f–h.

• 502.21b Objects with kicker have additional abilities that specify what happens if the kicker cost is paid. Objects with more than one kicker cost have abilities that correspond to each kicker cost.

• 502.21c If the text that depends on a kicker cost being paid targets one or more permanents and/or players, the spell’s controller chooses those targets only if he or she declared the intention to pay the appropriate kicker cost. Otherwise, the targets aren’t chosen at all.

• 502.21d A card with kicker may contain the phrases “if the [A] kicker cost was paid” and “if the [B] kicker cost was paid,” where A and B are the first and second kicker costs listed on the card, respectively. This text just refers to one kicker cost or the other, regardless of what the spell’s controller actually spent when paying the cost. In other words, read “if the [A] kicker cost was paid” as “if the first kicker cost listed was paid,” and read “if the [B] kicker cost was paid” as “if the second kicker cost listed was paid.”