Reap the Past

• WWizards of the Coast2019-06-14
  Official Ruling
  No player may take actions between the time the cards are chosen at random and the time they’re returned to your hand.
• WWizards of the Coast2019-06-14
  Official Ruling
  If X is greater than or equal to the number of cards in your graveyard, you simply return your entire graveyard to your hand.
• WWizards of the Coast2019-06-14
  Official Ruling
  All players get to see which cards you chose at random as they’re returned to your hand.
• WWizards of the Coast2019-06-14
  Official Ruling
  Reap the Past is still on the stack while you return cards to your hand, so it can’t return itself.

Rulings via Scryfall