More or Less — ruling 1

Indefinite articles such as “a” in “draw a card” aren’t number words and can’t be modified.

More or Less — ruling 2

You can’t change any instance of X.

More or Less — ruling 3

You can change the numeral inside of a mana symbol, but you can’t modify the cost of a spell in time to pay less for it. It must already be on the stack to be a valid target for More or Less.

More or Less — ruling 4

You can change power or toughness. If you change a toughness of 1 to 0, the creature will probably die.

More or Less — ruling 5

You can change the number of dice rolled for an effect only if the original instruction included a number word to describe how many dice to roll. You can’t change the “a” in “roll a six-sided die,” but you could change the “two” in “roll two six-sided dice.”

More or Less — ruling 6

You can change the number of sides on a die. If you don’t have any five-sided, seven-sided dice, or d21s handy, you can use other dice to simulate the rolls.

More or Less — ruling 7

You can turn a 0 into a -1. Sources that would deal 0 or less damage don’t deal any damage, even in silver-bordered games.

More or Less : règles, fonctionnement et interactions (MTG)

More or Less is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Add or subtract 1 or one from a number or number word on target spell or permanent until end of turn.

How it works : More or Less

Original English text — Wizards of the Coast / Scryfall

#1January 19, 2018· Wizards of the Coast
Indefinite articles such as “a” in “draw a card” aren’t number words and can’t be modified.
No other card is named in this ruling.
#2January 19, 2018· Wizards of the Coast
You can’t change any instance of X.
No other card is named in this ruling.
#3January 19, 2018· Wizards of the Coast
You can change the numeral inside of a mana symbol, but you can’t modify the cost of a spell in time to pay less for it. It must already be on the stack to be a valid target for More or Less.
No other card is named in this ruling.
#4January 19, 2018· Wizards of the Coast
You can change power or toughness. If you change a toughness of 1 to 0, the creature will probably die.
No other card is named in this ruling.
#5January 19, 2018· Wizards of the Coast
You can change the number of dice rolled for an effect only if the original instruction included a number word to describe how many dice to roll. You can’t change the “a” in “roll a six-sided die,” but you could change the “two” in “roll two six-sided dice.”
No other card is named in this ruling.
#6January 19, 2018· Wizards of the Coast
You can change the number of sides on a die. If you don’t have any five-sided, seven-sided dice, or d21s handy, you can use other dice to simulate the rolls.
No other card is named in this ruling.
#7January 19, 2018· Wizards of the Coast
You can turn a 0 into a -1. Sources that would deal 0 or less damage don’t deal any damage, even in silver-bordered games.
No other card is named in this ruling.