Historical Rules · 5 October 2018
Rule 508.4a
Official source text from the 5 October 2018 Rules release
If the effect that puts a creature onto the battlefield attacking specifies it’s attacking a certain player, and that player is no longer in the game when the effect resolves, the creature is put onto the battlefield but is never considered an attacking creature. The same is true if the effect specifies a creature is put onto the battlefield attacking a planeswalker and that planeswalker is no longer on the battlefield or is no longer a planeswalker when the effect resolves.