Historical Rules · 10 August 2018
Rule 103.6
Official source text from the 10 August 2018 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.”)