Historical Rules · 1 February 2012
Rule 715.5a
Official source text from the 1 February 2012 Rules release
At the end of a subgame of a Planechase game, the face-up plane card is turned face down and put on the bottom of its owner's planar deck. Then each player moves his or her planar deck from the subgame command zone to the main-game command zone and shuffles it.