I'm suspecting its Caribou tbh.
https://thiswriteguy.com/anime/one-piece/caribou-is-blackbeards-spy-in-wano-and-10th-commander/
Oda is giving him WAY too much screentime, making him a recurring character for over a decade now or so, across multiple arcs too but WHY?! What is the reason and the endgame with Oda and Caribou here?!
He knows about Shirhoshi being Poseidon too, I think he saw Momo get aged up by Shinobu too and god knows what else.
He has that weird "revolutionary hero" cover story that likened him to a doppelganger in-story who was like Che Guevara or so and he attacked Kaidos weapon factories so he could have gathered a ton of weapons? Didn't Blackbeard wantto gain weapons too?
Dragon mentioned quite a while ago now, that there are that new weapons being made from this "liquor ore" or something too. I suspected that it might have been to do with Wano and Kaido or at least Shanks potentially. Maybe Blackbeard will gain from this somehow too? Maybe with Caribous help?