Venom Blade Suit

The Black Death Sword was actually a symbiote as well, and the ancestor of all symbiotes. It had first been created by Knull from his own shadow. And shadows were, in a sense, a kind of "symbiote" with physical form. Later, after Knull used the Black Death Sword to slaughter the Celestials, he was banished to the abyssal dimension where it had been born. There, Knull used the severed skulls of the Celestials as a forge, continuously tempering the Black Death Sword and remaking it into the All-Black the Necrosword.