Add or subtract 1 or one from a number or number word on target spell or permanent until end of turn.
You canâ€™t change any instance of X.
You can turn a 0 into a -1. Sources that would deal 0 or less damage donâ€™t deal any damage, even in silver-bordered games.
You can change the numeral inside of a mana symbol, but you canâ€™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.
You can change the number of sides on a die. If you donâ€™t have any five-sided, seven-sided dice, or d21s handy, you can use other dice to simulate the rolls.
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 canâ€™t change the â€œaâ€ in â€œroll a six-sided die,â€ but you could change the â€œtwoâ€ in â€œroll two six-sided dice.â€
You can change power or toughness. If you change a toughness of 1 to 0, the creature will probably die.
Indefinite articles such as â€œaâ€ in â€œdraw a cardâ€ arenâ€™t number words and canâ€™t be modified.