Zernon has been made practically immortal by the will of fate. He is the lovechild of Order after all. Nothing would have worked to kill him deliberately had Zerkon not seen how to make Zernon fall. It had to be a betrayal that occurs when Zernon is at his absolute lowest. So Zerkon had to engineer a betrayal or several betrayals. His schemes have led them to this point. Now, Zerkon has to make Stelios finish the job that he started and kill Zernon.
He could have taken a more active part in the scheming but Zerkon is an observer, he can only look not interfere. It is the side effect of his abilities, he can't kill Zernon even if his Celestial Authority is strong enough to do it. Someone else has to fire the weapon and that person has to do it without being influenced by Zerkon.
He can place down the tools and set the situation in motion but his domain blocks him from doing more or else he will incur Karma and lose his powers. The contract of non-interference that he signed to get Zernon off his back made it certain that he can't be actively involved.
He didn't mind the contract too much. It allowed him to do what he does best. It allowed him to observe in peace. So he was able to see the impact of Legion's plans for the plane and insert himself within it.
Meanwhile Outside The Ball That The God Of Fate Has Become.
The first red specter to arrive raised its scythe and slashed at the large golden ball. The scythe passed through the gigantic ball without resistance. The specter stumbled forward before catching himself. Then the specter tried to touch the ball. The hand hit resistance and felt the ball. But the ball became intangible when the hand tried to scratch the ball with its claws.
The white flames within the eye sockets of the specter intensified after that observation.
Aeternus thought to himself. "This is bad. I can touch it but I can't hurt it. This is very bad."
His avatar isn't like those of the demon lord that can't do anything. The specters are created using his divine avatar ability by converting Godhood. This particular one has the strength of a grand god and the power of a sovereign, yet it cannot touch a Celestial.
More and more specters arrived and surrounded the ball. They tried everything they could but they can't hurt the ball in any way. They can see the large ball at all times and they can touch it. They can feel its existence but it becomes intangible anytime anything tries to hurt it.
Helios arrived soon after. He bombarded the ball with powerful solar energy but he got the same thing. His giant hand could touch the ball but he couldn't grasp it, lift it or move it in any way. The ball stood there uninfluenced by any action that can change it. It stood there like an imperious observer.
"This new god played us. This won't have happened had we been faster. He made sure that we will be delayed so that he can get here first." Aeternus observed calmly.
Helios said in agreement, "I could have gotten here earlier but things didn't work out as we thought. Stelios wasn't supposed to be part of the attack."
Killing a god is very difficult. You have to kill their main bodies if you want to kill a god. Killing an avatar won't do much to them. But the main body of gods is almost always within the divine plane and usually in their divine kingdoms. You have to go through a lot of trouble to kill a god of equal strength. It makes it not worth it unless you're an Origin god who can face the entire divine plane without a care in the world.
Even worse, a god can resurrect as long as their Godhood has not been refined by another person and they still have believers. Their divine soul and body will regenerate. So it is difficult to kill a god. Killing a Celestial is even more difficult. You have to destroy every bit of them and then refine their Godhood.
Helios couldn't kill Zernon in the divine plane even if he wants to and he is the strongest combatant of Legion in the plane. Demons can usurp a god's authority within their divine kingdom but Aeternus cannot kill Zernon since he is too weak for it. Aeternus is just a new demon king while Zernon is the Celestial Supreme and he has been for a very long time. So Legion looked for alternatives and they found one.
They predicted that the GodSlayer will be used against them if the gods were pushed to their limit. The weakness of gods is obvious. They will become desperate as long as you target their source of faith which is the mortals.
Mortals are usually safe from demons since they are in the mortal realm. But that changes if demons manage to bypass the divine plane. Then the gods will be forced to do anything they can to get rid of the threat.
There are limited options that will help the gods utilize their power in the mortal realm. First, there are vessels and then golems. The pantheon of Zargoth doesn't interact with the ancient battlefield and they don't have the technology themselves. That leaves the GodSlayer, a prototype weapon of ingenuity.
Legion planned to overwhelm those within the GodSlayer with stronger attacks that Aeternus will replicate. That method will injure Zernon the most or in case Zernon manages to escape, the attack will kill the other gods through the marks on their Godhood thereby leaving Zernon without help. Then Helios can swoop in with his fast speed and incapacitate him.
Things didn't go according to their plan because Helios was delayed in the mortal realm and it is all because of the god of fate's interference.