I doubt Poneglyghs are actually prophecy. There are many fake ones though. Since we already saw a DF that send people to the future, why doesn’t an opposite DF exist?
The Poneglygh in Fishman Island said that Joy Boy has to say apologize to Fishman Island because he broke the promise not to protect the island. And the Sea Kings said that their lord once a Mermaid and the moment Shirahoshi was born, she became their lord. I suspect, Shirahoshi, the mermaid princess now will be sent to the past since she knew about Luffy’s promise and being an “Ancient” Weapon, I believe there’s only one Ancient Weapon named Poseidon, it’s Shirahoshi.
I suspect one more person to be sent to the past, it’s Caribou, the mud dude. He was the man that was there to listen that Shirahoshi is the ancient weapon. And for some freaking reason he also was there to help Luffy at Wano, the place that produced Poneglyghs. I don’t think this is a coincidence.
But I can’t really tell who would be the one that send them to the past. It’s all about how the Poneglyghs on Laugh Tale go.
Why do I suspect this? It’s because of Toki, y’all remember when Toki first meet Oden? She said that she always wanted to visit Wano, despite she’s from the past. I believe she heard epic story about Joy Boy from someone in the past and wanted to visit Wano because of it.
Poneglyghs ain’t prophecies but actual stories from Facts. It’s not destiny or anything bs like that for Luffy. Luffy’s adventure is literally a random journey and was poneglygh-ed just like that