July 23, 2021 · Adventures in the Forgotten Realms
If you control multiple face-down spells or face-down permanents, you must ensure at all times that your face-down spells and permanents can be easily differentiated from each other. This includes, but is not limited to, knowing what ability or rules caused the permanents to be face down, the order spells were cast, the order that face-down permanents entered the battlefield, which creature(s) attacked last turn, and any other differences between face-down spells or permanents. Common methods for distinguishing between face-down objects include using counters or dice to mark the different objects, or clearly placing those objects in order on the table.
April 28, 2017 · Amonkhet
rule 708.6 not present in this release
May 1, 2013 · Dragon’s Maze
Some effects perform comparisons involving one or more split cards in a zone other than the stack or involving one or more fused split spells.
September 30, 2011 · Innistrad
Some effects perform comparisons involving characteristics of one or more split cards in a zone other than the stack.
June 17, 2011 · Commander 2011
Some effects perform comparisons involving characteristics of one or more split cards in a zone
February 4, 2011 · Mirrodin Besieged
Some effects perform comparisons involving characteristics of one or more split cards in a zone other than the stack.
October 1, 2010 · Scars of Mirrodin
Some effects perform comparisons involving characteristics of one or more split cards in a zone
February 1, 2010 · Worldwake
Some effects perform comparisons involving characteristics of one or more split cards in a zone other than the stack.