Wizened Arbiter

• WWizards of the Coast2019-11-12
  Official Ruling
  You don’t have to reveal the card in your hand that’s leaving the game.
• WWizards of the Coast2019-11-12
  Official Ruling
  If you have no cards in hand, you can’t put the white card you reveal into your hand.
• WWizards of the Coast2019-11-12
  Official Ruling
  In a casual game, a card you choose from outside the game comes from your personal collection. In a tournament event, a card you choose from outside the game must come from your sideboard. You may look at your sideboard at any time.

Rulings via Scryfall