For those watching The Rise of Skywalker, you may be quite curious as to the opening crawl beginning with something that happens off-screen:
The dead speak! The galaxy has heard a mysterious broadcast, a threat of REVENGE in the sinister voice of the late EMPEROR PALPATINE.
So what is this broadcast?
Well, it doesn’t appear at all in the movie, nor do we even know what the content of the message is from references to it.
However, it has appeared in Fortnite, where one hears Palpatine declaring,
At last, the work of generations is complete. The great error is corrected: the day of victory is at hand; the day of revenge; the day of the Sith!
It is certainly cryptic and anyone in the Star Wars galaxy hearing it may certainly doubt that it emanated from Palpatine, having thought him dead since the Battle of Endor.
However, as we see from the events of The Rise of Skywalker, this message did, indeed, emanate from the still-alive Palpatine.