Really? I saw the raw of that mural. The monster didn't look like Blackbeard, Oda is probably playing with the readers. The mermaid (Shirahoshi) annoyed me though.
Hit up that megathread, or the chapter thread, there's a lot of posts on that mural.
Me personally I'm quite convinced the " will never/ will surely meet again" lines at the end of each verse is referring to Blackbeard and Luffy meeting. I think BB isn't from Earth or something, the phrase says something about half crescent people and full moon people, I think half crescent are earthlings and the others from the forbidden star (Moon?) left the planet in the First World.
There was a picture of kid Teach crying under a half crescent (fragmented) moon - my interpretation is he was longing to reach it/the people there.
Also the sea creatures in Wano during Oden's flashback were talking about two individuals meeting again, and they were talking about them needing more time to be born and more time to grow strong enough. Seems like a reference to the same thing.
Also I think the right side and the left side of the mural are both events that already happened in the past. On the left is the 2nd war with Imu fighting Joyboy and his allies.
I don't think the 3rd world is depicted on there.
Dw I will read yours too when I have the appetite for it
@kyejames316