Grunn, the Lonely King

Doubling a creature’s power and/or toughness creates a continuous effect. This effect modifies that creature’s power and/or toughness but doesn’t set those characteristics to a specific value. See rule 613.4c.

To double a creature’s power, that creature gets +X/+0, where X is that creature’s power as the spell or ability that doubles its power resolves. Similarly, an effect that doubles a creature’s toughness gives it +0/+X, where X is that creature’s toughness. Doubling a creature’s power and toughness gives it +X/+Y, where X is its power and Y is its toughness.

If a creature’s power is less than 0 when it’s doubled, doubling that creature’s power instead means that the creature gets -X/-0, where X is the difference between 0 and its power. Similarly, if its toughness is less than 0 when doubled, it gets -0/-X. If one characteristic’s value is negative but the other isn’t when both are doubled, it gets -X/+Y or +X/-Y, as appropriate.

To double a player’s life total, the player gains or loses an amount of life such that their new life total is twice its current value.

To double the number of a kind of counters on a player or permanent, give that player or permanent as many of those counters as that player or permanent already has.

To double the amount of a type of mana in a player’s mana pool, that player adds an amount of mana of that type equal to the amount they already have.

To double an amount of damage a source would deal, that source instead deals twice that much damage. This is a replacement effect.

Kicker is a static ability that functions while the spell with kicker is on the stack. “Kicker [cost]” means “You may pay an additional [cost] as you cast this spell.” Paying a spell’s kicker cost(s) follows the rules for paying additional costs in rules 601.2b and 601.2f–h.

The phrase “Kicker [cost 1] and/or [cost 2]” means the same thing as “Kicker [cost 1], kicker [cost 2].”

Multikicker is a variant of the kicker ability. “Multikicker [cost]” means “You may pay an additional [cost] any number of times as you cast this spell.” A multikicker cost is a kicker cost.

If a spell’s controller declares the intention to pay any of that spell’s kicker costs, that spell has been “kicked.” If a spell has two kicker costs or has multikicker, it may be kicked multiple times. See rule 601.2b.

Objects with kicker or multikicker have additional abilities that specify what happens if they were kicked. These abilities are linked to the kicker or multikicker abilities printed on that object: they can refer only to those specific kicker or multikicker abilities. See rule 607, “Linked Abilities.”

Objects with more than one kicker cost may also have abilities that each correspond to a specific kicker cost. Those abilities contain the phrases “if it was kicked with its [A] kicker” and “if it was kicked with its [B] kicker,” where A and B are the first and second kicker costs listed on the card, respectively. Each of those abilities is linked to the appropriate kicker ability.

If part of a spell’s ability has its effect only if that spell was kicked, and that part of the ability includes any targets, the spell’s controller chooses those targets only if that spell was kicked. Otherwise, the spell is cast as if it did not have those targets. See rule 601.2c.

Sticker kicker is a keyword ability that represents a kicker ability and an ability that imposes an additional cost if the spell is kicked. “Sticker kicker [cost]” means “Kicker [cost]” and “As an additional cost to cast this spell, if it’s kicked, you get a ticket counter and you may put a sticker on this spell.”