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 the power and/or toughness of a creature or creature card.
107.1c If a rule or ability instructs a player to choose “any number,” that player may choose any positive number or zero.
107.2. If anything needs to use a number that can’t be determined, either as a result or in a calculation, it uses 0 instead.
107.3. Many objects use the letter X as a placeholder for a number that needs to be determined. Some objects have abilities that define the value of X; the rest let their controller choose the value of X.
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 If a spell or ability refers to the {X} or X in the mana cost, alternative cost, additional cost, or activation cost of another object, any X in that spell or ability’s text uses the value of X chosen or defined for the other object.
107.3f 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).
107.3g 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.
107.3h 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.
107.3i Normally, all instances of X on an object have the same value at any given time.
107.3j 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 107.3i. This may occur with ability-adding effects, text-changing effects, or copy effects.
107.3k If an object’s activated ability has an {X}, [-X], or X in its activation cost, the value of X for that ability is independent of any other values of X chosen for that object or for other instances of abilities of that object. This is an exception to rule 107.3i.
107.3m 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 107.3i.
107.3n Some objects use the letter Y in addition to the letter X. Y follows the same rules as X.
107.4. The mana symbols are {W}, {U}, {B}, {R}, {G}, and {C}; the numerical symbols {0}, {1}, {2}, {3}, {4}, and so on; the variable symbol {X}; the hybrid symbols {W/U}, {W/B}, {U/B}, {U/R}, {B/R}, {B/G}, {R/G}, {R/W}, {G/W}, and {G/U}; the monocolored hybrid symbols {2/W}, {2/U}, {2/B}, {2/R}, and {2/G}; the Phyrexian mana symbols {W/P}, {U/P}, {B/P}, {R/P}, and {G/P}; and the snow mana symbol {S}.
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.
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.
107.4g In rules text, the Phyrexian symbol {P} with no colored background means any of the five Phyrexian mana symbols.
107.4h When used in a cost, the snow mana symbol {S} represents a cost that can be paid with one mana of any type produced by a snow source (see rule 106.3). Effects that reduce the amount of generic mana you pay don’t affect {S} costs. The {S} symbol can also be used to refer to mana of any type produced by a snow source spent to pay a cost. Snow is neither a color nor a type of mana.
107.5. The tap symbol is {T}. The tap symbol in an activation cost means “Tap this permanent.” A permanent that’s already tapped can’t be tapped again to pay the cost. A creature’s activated ability with the tap symbol in its activation cost can’t be activated unless the creature has been under its controller’s control continuously since their most recent turn began. See rule 302.6.
107.6. The untap symbol is {Q}. The untap symbol in an activation cost means “Untap this permanent.” A permanent that’s already untapped can’t be untapped again to pay the cost. A creature’s activated ability with the untap symbol in its activation cost can’t be activated unless the creature has been under its controller’s control continuously since their most recent turn began. See rule 302.6.
107.7. Each activated ability of a planeswalker has a loyalty symbol in its cost. Positive loyalty symbols point upward and feature a plus sign followed by a number. Negative loyalty symbols point downward and feature a minus sign followed by a number or an X. Neutral loyalty symbols don’t point in either direction and feature a 0. [+N] means “Put N loyalty counters on this permanent,” [-N] means “Remove N loyalty counters from this permanent,” and [0] means “Put zero loyalty counters on this permanent.”
107.8. The text box of a leveler card contains two level symbols, each of which is a keyword ability that represents a static ability. The level symbol includes either a range of numbers, indicated here as “N1-N2,” or a single number followed by a plus sign, indicated here as “N3+.” Any abilities printed within the same text box striation as a level symbol are part of its static ability. The same is true of the power/toughness box printed within that striation, indicated here as “[P/T].” See rule 710, “Leveler Cards.”
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 base 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 base power and toughness [P/T] and has [abilities].”
107.9. A tombstone icon appears to the left of the name of many Odyssey™ block cards with abilities that are relevant in a player’s graveyard. The purpose of the icon is to make those cards stand out when they’re in a graveyard. This icon has no effect on game play.
107.10. A type icon appears in the upper left corner of each card from the Future Sight® set printed with an alternate “timeshifted” frame. If the card has a single card type, this icon indicates what it is: claw marks for creature, a flame for sorcery, a lightning bolt for instant, a sunrise for enchantment, a chalice for artifact, and a pair of mountain peaks for land. If the card has multiple card types, that’s indicated by a black and white cross. This icon has no effect on game play.
107.11. The Planeswalker symbol is {PW}. It appears on one face of the planar die used in the Planechase casual variant. See rule 901, “Planechase.”
107.12. The chaos symbol is {CHAOS}. It appears on one face of the planar die used in the Planechase casual variant, as well as in abilities that refer to the results of rolling the planar die. See rule 901, “Planechase.”
107.13. A color indicator is a circular symbol that appears to the left of the type line on some cards. The color of the symbol defines the card’s color or colors. See rule 202, “Mana Cost and Color.”
107.14. The energy symbol is {E}. It represents one energy counter. To pay {E}, a player removes one energy counter from themselves.
107.15. The text box of a Saga card contains chapter symbols, each of which is a keyword ability that represents a triggered ability. A chapter symbol includes a Roman numeral, indicated here as “rN”. The text printed in the text box striation to the right of a chapter symbol is the effect of the triggered ability it represents. See rule 714, “Saga Cards.”
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].”