When an effect puts one or more cards into a graveyard at the same time, the owner of those cards determines the order that they are placed there. This is true when multiple cards would go to the graveyard from any zone, such as when discarding cards or when putting cards directly from your library into your graveyard (perhaps due to Dredge or Sword of Body and Mind). For example, when Day of Judgment resolves, all creatures in play are destroyed. Each player will be able to determine the order that these cards are placed in his or her graveyard.

In the vast majority of cases, this does not have any significant impact on game play; however, for formats that allow sets prior to Urza’s Saga, there are a few implications. Nether Shadow, Death Spark and Ashen Ghoul are all examples of cards with abilities that depend on graveyard order. When playing formats that allow these cards (Vintage, Legacy and certain block formats), it is important that graveyard order be maintained.

Finally, this rule also applies when one or more cards go to a player’s library as well. When Plow Under resolves, the owner of those cards determines the order that they are placed on top of his or her library (and because the cards are going to a hidden zone, you don’t have to show your opponent the order you choose).