Historical Rules · 29 April 2022
Rule 722.5a
Official source text from the 29 April 2022 Rules release
At the end of a subgame of a Planechase game, each face-up plane card or phenomenon card is turned face down and put on the bottom of its owner’s planar deck. Then each player moves their planar deck from the subgame command zone to the main-game command zone and shuffles it.