Historical Rules · 29 September 2017
Rule 115.2g
Official source text from the 29 September 2017 Rules release
In a Planechase game, rolling the planar die is a special action. A player can take this action any time he or she has priority and the stack is empty during a main phase of his or her turn. Taking this action costs a player an amount of mana equal to the number of times he or she has previously taken this action on that turn. Note that this number won’t be equal to the number of times the player has rolled the planar die that turn if an effect has caused the player to roll the planar die that turn. See rule 901, “Planechase.”