Blackbone Theory
So I don't have any sources to cite, at the moment, Im at work and just had this thought and needed to get it out. So we know the Gods-From-Blood and the Gods-From-Flesh supplanted the Gods-From-Stone, specifically, the Red Grail is said to have drank the Tide until nothing remained. The Blackbone, from what we know, is tied to whale falls, decay that leads to new growth, decay in appetite, in sustenance. What if the Red Grail took her current portfolio of domains from the Tide and left it exsanguinated and skeletal, tied only to death and feeding life with death. Could the Blackbone be whats left of the Tide? Im not sure if anyone else has made this connection and I also don't know if there are any lore implications that lead to this, but it popped into my head today.