Historical Rules · 7 August 2020
Rule 103.6
Official source text from the 7 August 2020 Rules release
In a Planechase game, the starting player moves the top card of their planar deck off that planar deck and turns it face up. If it’s a phenomenon card, the player puts that card on the bottom of their planar deck and repeats this process until a plane card is turned face up. The face-up plane card becomes the starting plane. (See rule 901, “Planechase.”)