Richard Garfield, Ph.D.

• WWizards of the Coast2020-02-29
  Official Ruling
  By default, you are limited to cards legal in the format you’re playing. If you’re playing Draft or Sealed Deck, you can name any card available in the format you’re playing. If you’re playing with Unsanctioned decks, anything goes. Discuss with your playgroup if you’d prefer to modify or eliminate these limitations.
• WWizards of the Coast2020-02-29
  Official Ruling
  Playing cards as though they were other cards is optional.
• WWizards of the Coast2020-02-29
  Official Ruling
  Richard Garfield, Ph.D. essentially makes you play a variant of the Magic game called “Mental Magic.” Here’s how the game works. Whenever you cast a spell, you reveal the card to all players and choose any other card (see below for the cards that you can use) that has that card’s mana cost. (Note that color very much does matter.) That spell can then be cast as though it was the chosen card. You aren’t allowed to choose the same card twice.
• WWizards of the Coast2020-02-29
  Official Ruling
  The same is true if Richard Garfield, Ph.D. changes controllers. If you play a Savannah Lions as Swords to Plowshares, then an opponent gains control of Richard Garfield, Ph.D., that player can then do the same.
• WWizards of the Coast2020-02-29
  Official Ruling
  If more than one player controls a Richard Garfield, Ph.D., the cards one player plays has no effect on the other players. For example, each player could play Savannah Lions as a Swords to Plowshares this way.
• WWizards of the Coast2020-02-29
  Official Ruling
  Each Richard tracks its own list of played cards. If one leaves the battlefield and another enters, cards previously played under the first Richard are available once again.

Rulings via Scryfall