(Dominaria Spoilers) Can the new buy-a-box-promo card deal damage to Planeswalkers?
In early March, the release notes were accidentally published in Simplified Chinese, and Wizards of the Coast responded to that leak by publishing the release notes in all languages. In the release notes, the section about the planeswalker damage redirection rules change includes the following paragraph:


  Cards printed in the Dominaria set that deal damage to creatures and/or players but not to planeswalkers (such as the Planeswalker Deck card Chandra, Bold Pyromancer and the promotional card Firesong and Sunspeaker) require targets as written even though similar cards have received errata.


In addition, the release notes list the text of Firesong and Sunspeaker as follows:


  Firesong and Sunspeaker (Buy-a-Box Promotional Card)
  4RW
  Legendary Creature – Minotaur Cleric
  4/6
  Red instant and sorcery spells you control have lifelink.
  Whenever a white instant or sorcery spell causes you to gain life, Firesong and Sunspeaker deals 3 damage to target creature or player.


and includes this ruling


  The last ability of Firesong and Sunspeaker can't target a planeswalker.