Simply put, Andrew's ability was an application of the world's rules. The reason he used it on Chthon was, on one hand, to test this ability.
After all, using this ability on ordinary people and using it on the powerful were two completely different matters. Since Andrew wanted to treat it as a Trump Card, he naturally had to test it on a powerful opponent.
The Great Demon God was undoubtedly the best target, because Chthon would be Andrew's ultimate enemy.
On the other hand, it was to strengthen the Curse's effect. The Data Curse Andrew created with the Great Demon God as its core was already immensely powerful. With this ability added on top, it could even muddle Chthon's perception.
For example, Chthon's Trump Card might originally be too weak to kill the King of Abilities. Once his perception was muddled, it would become capable of killing the King of Abilities. When the time came, it would be impossible for him not to lose.
As for why he told the Great Demon God about this, that was one of the Curse's requirements. Curses often had conditions that needed to be fulfilled before they could be used. The more conditions fulfilled, the stronger the Curse.
"What, are you afraid this will get out? There are only the Mechanical Demon King, the King of Abilities, and the Great Demon God here. How could it get out? The Great Demon God's connection with Chthon, as well as with his main body, is under Andrew's control."
As for the two Kings of Negativity, one had its self-awareness erased, while the other had become Curse material. Neither could sense what was happening outside anymore.
"All right, I've told you everything you need to know, Great Demon God. Serve me well from now on and