As we can see in the picture it's the Cerberus a creature that represents Blackbeard's devil fruit power. Cerberus has 3 colors Black, White and Red; as Black represents the Yami Yami No Mi; White represents the Gura Gura No Mi; and lastly his third will be the Mera Mera No Mi the DF that Sabo had. As Cerberus is from Underworld creature and Underworld consist of Darkness "Yami Yami No Mi", river of Fire "Mera Mera No Mi" and Hades wants destruction "Gura Gura No Mi". Hades Represents Blackbeard itself that has a pet Cerberus and it's all connect to the fact that it's possible that the thrid DF of Blackbeard will be the Mera Mera No Mi. And that point Sabo will be dead.