Causality killing strikes, though indeed unfair, first require overwhelming strength!
With his Fourth Layer Heaven peak methods, launching a causality killing strike through the interface avatar to remotely kill a True God of the Three Layers Heavenly, he indeed had a chance. But against an existence of the same Fourth Layer Heaven, it was useless.
What's more, Chen Mu relied on a strike that merged the Origin Power of the Void, Time, and Creation to forcibly obliterate the causality killing strike he had prepared for a while. Needless to say, even attacking Chen Mu's interface avatar was beyond his capabilities.
"To deal with a small boundary in these remote frontiers like mine, even a Fourth Layer Heaven figure came. It truly shows some regard for my world... However, this is ultimately the Fan Gu Space Domain, the territory governed by the Fan Gu Divine Monarch. Does your Demon Clan really not care about the majesty of the Fan Gu Divine Monarch by rampaging so wantonly?"