Rulings

• The creature blocks only if it's able to do so as the declare blockers step begins. If, at that time, the creature is tapped, it's affected by a spell or ability that says it can't block, or no creatures are attacking its controller or a planeswalker controlled by that player, then it doesn't block. If there's a cost associated with having the creature block, the player isn't forced to pay that cost. If that cost isn't paid, the creature won't block.2021-04-16
• The controller of the creature chooses which attacking creature that creature blocks.2021-04-16
• You choose whether you want the creature to gain reach until end of turn as Academic Dispute resolves.2021-04-16
• If a card is brought into the game from outside the game, it will stay in the game until it ends or until its owner leaves the game, whichever comes first.2021-04-16
• If you bring a card into the game from outside the game in a Constructed tournament (or a Constructed game played under tournament conditions), you may select only a card from your sideboard. In casual Constructed games, the card comes from your collection.2021-04-16
• If you bring a card into the game from outside the game in a Sealed Deck or Booster Draft event, you may select only a card that is in the card pool that you built your deck from.2021-04-16
• If instructed to learn, you may do nothing. Discarding a card and putting a Lesson card into your hand are both optional.2021-04-16