Some effects instruct a player to “play” with a certain aspect of the game changed, such as “Play with the top card of your library revealed.” “Play” in this sense means to play the Magic game.
July 3, 2020 · Core Set 2021
If multiple players scry at once, each of those players looks at the top cards of their library at the same time. Those players decide in APNAP order (see rule 101.4) where to put those cards, then those cards move at the same time.
May 3, 2019 · War of the Spark
If a player is instructed to search a hidden zone for cards that match an undefined quality, that player may still search that zone but can’t find any cards.
January 25, 2019 · Ravnica Allegiance
If a player is instructed to search a hidden zone for cards that match an undefined quality, that player may still search that zone but can't find any cards.
April 27, 2018 · Dominaria
If a player is instructed to search a hidden zone for cards that match an undefined quality, that player may still search that zone but can’t find any cards.
September 30, 2016 · Kaladesh
If an effect would cause a player to shuffle one or more specific objects into a library, that library is shuffled even if none of those objects are in the zone they’re expected to be in or an effect causes all of those objects to be moved to another zone or remain in their current zone.