Symbiotes were derivatives of Knull, and Knull was the embodiment of the Living Abyss. Naturally, Knull's body could unfurl and spread like a symbiote, then envelop other living beings. The Black King chose this method to attack Peter.
So, what use was it?
The answer was that it was completely useless.
In an instant, the dazzling radiance of the Enigma Force shot beams in every direction, completely piercing through the encroaching Living Abyss. But that was precisely what the Black King intended. He wanted Peter to make the only viable choice, allowing him to launch his next attack.
As a result, he struck nothing.
Spider-Man seemed to vanish completely in an instant, fleeing directly without even bothering to take the Dragonfang Sword.
Sling Ring portals appeared one after another around him, but Peter Parker did not emerge from any of them. The Black King immediately extended countless symbiote tendrils and thrust them into the portals in search of Spider-Man, but found nothing. Instead, the portals closed in an instant, severing those tendrils outright.
Yet when the Black King sensed the locations of those tendrils, he found that they were scattered across every corner of the universe, with no pattern whatsoever. He could not determine Peter's location based solely on what lay beyond the portals.
Where had he gone?
Unable to find Peter anywhere, the Black King began to think. His first thought was whether the other man had fled. In theory, Spider-Man, wielding the power of Captain Universe, could indeed escape, and given that there was no especially deep conflict between them, there was little need for him to stop Peter if he wanted to leave. So it made perfect sense if he had gone back to Earth-616, didn't it?
But the Black King did not leave with that assumption.