Rule 706.1 · Rolling a Die
An effect that instructs a player to roll a die will specify what kind of die to roll and how many of those dice to roll.
Subrules
Such an effect may refer to an “N-sided die,” “N-sided dice,” or one or more “dN,” where N is a positive integer. In those cases, the die must have N equally likely outcomes, numbered from 1 to N. For example, a d20 is a twenty-sided die with possible outcomes from 1 to 20.
Players may agree to use an alternate method for rolling a die, including a digital substitute, as long as the method used has the same number of equally likely outcomes as the die specified in the instruction.