Delirium Skeins

• WWizards of the Coast2017-03-14
  Official Ruling
  When Delirium Skeins resolves, first the player whose turn it is chooses three cards to discard, then each other player in turn order chooses three cards to discard, then all of those cards are discarded simultaneously. No one sees what the other players are discarding before deciding which cards to discard.

Rulings via Scryfall