Rule 901.5 · Planechase

Once all players have kept their opening hands and used the abilities of cards that allow them to take an action with those cards from their opening hands, 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. (See rule 103.7.) No abilities of any card turned face up this way trigger during this process. The face-up plane card becomes the starting plane.