Promise of Power

• WWizards of the Coast2004-10-04
  Official Ruling
  The power/toughness of the token is set when this spell resolves.
• WWizards of the Coast2004-12-01
  Official Ruling
  The power and toughness of the Demon token are set when Promise of Power resolves. They’re unaffected if the number of cards in your hand changes later.
• WWizards of the Coast2004-12-01
  Official Ruling
  If you pay the entwine cost, you draw five cards, then lose five life, then put the Demon token onto the battlefield. The five cards you draw count toward the Demon’s power and toughness.

Rulings via Scryfall