Board Thread:General Discussion/@comment-1031724-20160318030639

There has been plenty of talk but I think I know what it means, though I got help from other users here in this.

As we all know, against all odds, Bill Cipher was the one to die in the series finale of Gravity Falls (though it was originally intended to be Mabel). As he is being erased inside Stan's mind, he says a message which, played backwards, says "A X O L O T L! My time has come to burn! I invoke the ancient power that I may return." Then Stan destroys him with a punch.

What I think is:

In-universe: Bill was just trying to compose himself by convincing himself that he would return, even though he knew he wouldn't, as his powers weren't working inside Stan's mind while it was being erased. Playing the message backwards, you can hear him sound increasingly desperate, which of course would be how he started out.

Out of universe: You know the show likes to be mysterious. They're probably teasing us with a possibility that he might return, probably as a reference to people speculating that villains will return even after they're dead (like King Sombra in MLP) and making us wonder what that means.

And of course we can't expect a Bill return in future episodes when of course there are no future episodes, this was series finale. 