There have always been two forces in the universe at war. Darkness and Light. (yeah I know it sounds like a chinese novel but that is what is in the comics. Or at least roughly to the same extent). Darkness prevailed for a long time and soon manifested itself on the body of Knull workings a symbiote.
Guiding him, giving him power. But all of this changed when the Celestials came and took over his kingdom. They waged war on him and everything he held dear to, was stripped away. Later he made the All-Black but that was still not enough to defeat the Celestials.
And when he thought he would conquer the world slowly, he was beaten down again, and this time, it was his arch enemy.
The Light.
When Darkness ruled when Light was in its infancy, the invasion of Celestials just made the growing process of Light faster. The symbiotes had always been under Knull's rule but once they were touched by Light, his plans went to shit. His dear symbiotes revolted against him and later imprisoned him, in his own place.
The influence of Darkness also went down and all he could do was bide his time and grow stronger. Darkness could never be eradicated totally. This was the law. The same law applied to Light too. But Knull wanted to change it, and bring the multiverse back to the Abyss. His kingdom!!
Now he was here. To take everything back. The place where it all started (Thor was the first to defeat Grendel, one of the first symbiote dragons. Grendel's defeat started the process of infusing Light into the symbiotes, it was on Earth 616 where it all started.)
"You seem to know a lot. Were you the one who was trying to sneak up on me all this time after I was awake?" Knull spoke in a very metallic tone. His figure looked exactly like the comics. At least 8 feet in height. Made of nothing but bones and skin attached to it. He didn't seem like there was blood in his veins. His eyes had pitch black color with occasional red hues on them.
His face, like his body, didn't have muscle and had sharp teeth, like the piranhas. All-in-all, atypical zombie villain. Behind him was a longsword.
"I did. At least I tried to. But it seems Darkness didn't allow me."
"I smell the same breath as those filthy beings. I will take immense pleasure in making you one of my symbiote hosts."
"Oh!! With what? Two of the symbiote Celestials that you have been hiding? You should have remained asleep at Klyntar. Sleep is the best thing ever. Why wake up?" John taunted him. He had no fear. Sure, Knull was powerful but it never meant that John was a weakling. Knull, for the first time, had a look of surprise.
Him having the Celestials was a trump card, a card he could pull if Light ever showed up. But now this person seemed like he knew everything. Out of anger, Knull without saying another word made a swiping motion at John.
Using the All-Black. A jet black ray traveled through the distance and approached John. The others seeing this were ready to take action to stop the attack from reaching them, but John made the motion with his hand to not interfere. He had a perfect way to stop this.
The black ray after approaching John and his team suddenly vanished. It was as if all the attacks never existed in the first place. The other members of 616-Avengers were skeptical about Knull's attack first.
They were ready to stop it, but seeing that none of their companions took action, they stopped. They wanted to see how the enigmatic 'John Jameson' would react. And they were not disappointed. The attack itself vanished.
Knull was surprised too by this. Not because the attack was stopped. He already knew what would happen. This attack was just a probing attack. He was surprised by the way the attack had vanished.
The power of Time!!
He looked at the person who did it. Yhwach. Knull looked at Yhwach, for the first time in his entire life, and felt a little cold. It was as if he was looking at the Abyss again. And this Abyss was inside a person.
"You can control time?" Knull spoke. Yhwach just looked at him and didn't reply. Instead he extended his hand. And the next moment, a huge shining bright sword was in his hand.
This sword looked like it was made of light itself. The light was too white, looked too pure, too bright. The sword looked like it was illuminating in this place and giving light everywhere.
"This isn't Light. What are you?" Knull spoke in a more serious tone now. Though the sword was not made of the same Light he had always known.
This light seemed cruel and menacing to him. It was as if this light could obliterate souls. Or in this case, their connections to the Codex.