- 107.1 The only numbers the Magic game uses are integers.
- 107.1a You can’t choose a fractional number, deal fractional damage, gain fractional life, and so on. If a spell or ability could generate a fractional number, the spell or ability will tell you whether to round up or down.
- 107.1b Most of the time, the Magic game uses only positive numbers and zero. You can’t choose a negative number, deal negative damage, gain negative life, and so on. However, it’s possible for a game value, such as a creature’s power, to be less than zero. If a calculation or comparison needs to use a negative value, it does so. If a calculation that would determine the result of an effect yields a negative number, zero is used instead, unless that effect doubles or sets to a specific value a player’s life total or a creature’s power and/or toughness.
Example: If a 3/4 creature gets -5/-0, it’s a -2/4 creature. It doesn’t assign damage in combat. Its total power and toughness is 2. Giving it +3/+0 would raise its power to 1.
Example: Viridian Joiner is a 1/2 creature with the ability “{T}: Add an amount of {G} equal to Viridian Joiner’s power.” An effect gives it -2/-0, then its ability is activated. The ability adds no mana to your mana pool.
Example: Chameleon Colossus is a 4/4 creature with the ability “{2}{G}{G}: Chameleon Colossus gets +X/+X until end of turn, where X is its power.” An effect gives it -6/-0, then its ability is activated. Its power and toughness remains a -2/4 creature. It doesn’t become -4/2.
- 107.1c If a rule or ability instructs a player to choose “any number,” that player may choose any positive number or zero.
- 107.3a If a spell or activated ability has a mana cost, alternative cost, additional cost, and/or activation cost with an {X}, [-X], or X in it, and the value of X isn’t defined by the text of that spell or ability, the controller of that spell or ability chooses and announces the value of X as part of casting the spell or activating the ability. (See rule 601, “Casting Spells.”) While a spell is on the stack, any X in its mana cost or in any alternative cost or additional cost it has equals the announced value. While an activated ability is on the stack, any X in its activation cost equals the announced value.
- 107.3b If a player is casting a spell that has an {X} in its mana cost, the value of X isn’t defined by the text of that spell, and an effect lets that player cast that spell while paying neither its mana cost nor an alternative cost that includes X, then the only legal choice for X is 0. This doesn’t apply to effects that only reduce a cost, even if they reduce it to zero. See rule 601, “Casting Spells.”
- 107.3c If a spell or activated ability has an {X}, [-X], or X in its cost and/or its text, and the value of X is defined by the text of that spell or ability, then that’s the value of X while that spell or ability is on the stack. The controller of that spell or ability doesn’t get to choose the value. Note that the value of X may change while that spell or ability is on the stack.
- 107.3d If a cost associated with a special action, such as a suspend cost or a morph cost, has an {X} or an X in it, the value of X is chosen by the player taking the special action immediately before they pay that cost.
- 107.3e Sometimes X appears in the text of a spell or ability but not in a mana cost, alternative cost, additional cost, or activation cost. If the value of X isn’t defined, the controller of the spell or ability chooses the value of X at the appropriate time (either as it’s put on the stack or as it resolves).
- 107.3f If a card in any zone other than the stack has an {X} in its mana cost, the value of {X} is treated as 0, even if the value of X is defined somewhere within its text.
- 107.3g If an effect instructs a player to pay an object’s mana cost that includes {X}, the value of X is treated as 0 unless the object is a spell on the stack. In that case, the value of X is the value chosen or determined for it as the spell was cast.
- 107.3h Normally, all instances of X on an object have the same value at any given time.
- 107.3i If an object gains an ability, the value of X within that ability is the value defined by that ability, or 0 if that ability doesn’t define a value of X. This is an exception to rule 107.3h. This may occur with ability-adding effects, text-changing effects, or copy effects.
- 107.3k If an object’s enters–the–battlefield triggered ability or replacement effect refers to X, and the spell that became that object as it resolved had a value of X chosen for any of its costs, the value of X for that ability is the same as the value of X for that spell, although the value of X for that permanent is 0. This is an exception to rule 107.3h.
- 107.3m Some objects use the letter Y in addition to the letter X. Y follows the same rules as X.
- 107.4a There are five primary colored mana symbols: {W} is white, {U} blue, {B} black, {R} red, and {G} green. These symbols are used to represent colored mana, and also to represent colored mana in costs. Colored mana in costs can be paid only with the appropriate color of mana. See rule 202, “Mana Cost and Color.”
- 107.4b Numerical symbols (such as {1}) and variable symbols (such as {X}) represent generic mana in costs. Generic mana in costs can be paid with any type of mana. For more information about {X}, see rule 107.3.
- 107.4c The colorless mana symbol {C} is used to represent one colorless mana, and also to represent a cost that can be paid only with one colorless mana.
- 107.4d The symbol {0} represents zero mana and is used as a placeholder for a cost that can be paid with no resources. (See rule 118.5.)
- 107.4e Hybrid mana symbols are also colored mana symbols. Each one represents a cost that can be paid in one of two ways, as represented by the two halves of the symbol. A hybrid symbol such as {W/U} can be paid with either white or blue mana, and a monocolored hybrid symbol such as {2/B} can be paid with either one black mana or two mana of any type. A hybrid mana symbol is all of its component colors.
Example: {G/W}{G/W} can be paid by spending {G}{G}, {G}{W}, or {W}{W}.
- 107.4f Phyrexian mana symbols are colored mana symbols: {W/P} is white, {U/P} is blue, {B/P} is black, {R/P} is red, and {G/P} is green. A Phyrexian mana symbol represents a cost that can be paid either with one mana of its color or by paying 2 life.
Example: {W/P}{W/P} can be paid by spending {W}{W}, by spending {W} and paying 2 life, or by paying 4 life.
- 107.4g In rules text, the Phyrexian symbol {P} with no colored background means any of the five Phyrexian mana symbols.
- 107.4h The snow mana symbol {S} represents one mana in a cost. This mana can be paid with one mana of any type produced by a snow permanent (see rule 205.4g). Effects that reduce the amount of generic mana you pay don’t affect {S} costs. Snow is neither a color nor a type of mana.
- 107.8a “{LEVEL N1-N2} [Abilities] [P/T]” means “As long as this creature has at least N1 level counters on it, but no more than N2 level counters on it, it has power and toughness [P/T] and has [abilities].”
- 107.8b “{LEVEL N3+} [Abilities] [P/T]” means “As long as this creature has N3 or more level counters on it, it has power and toughness [P/T] and has [abilities].”
- 107.15a “{rN}—[Effect]” means “When one or more lore counters are put onto this Saga, if the number of lore counters on it was less than N and became at least N, [effect].”
- 107.15b “{rN1}, {rN2}—[Effect]” is the same as “{rN1}—[Effect]” and “{rN2}—[Effect].”