Many in the Gravity Falls fandom have speculated that Bill Cipher and Grunkle Stan might be one and the same person. The Axolotl poem usually comes up, as well as very specific choice of words used both by Bill and Stan (Buy gold. Eenie-meenie-minie-you! And so on). We know that Bill has found a way out of certain death in the series finale, by invoking the name of the Axolotl. This, contrasted with the aforementioned poem found in Dipper and Mabel and the Curse of the Time Pirates' Treasure sheds light upon a much deeper connection between the entity that Bill Cipher is and the man who is Mr. Mystery for a reason.
Sixty degrees that come in threes.
Watches from within birch trees.
Saw his own dimension burn.
Misses home and can't return.
Says he's happy. He's a liar.
Blame the arson for the fire.
If he wants to shirk the blame,
He'll have to invoke my name.
One way to absolve his crime.
A different form, a different time.
By deconstructing the poem l