Since Black Ghost Fire doesn't emit normal heat when burning something, Bai Luoran didn't suspect that Mo Huasong used fire to burn her longsword.
Mo Huasong bashfully chuckled, but didn't show it. "Old woman, it's your fault for using inferior weapons. You can't even break the weapons from our mundane world."
"Inferior weapons? Let me tell you, these are magic artifacts refined by our Cultivation Realm's Refining Equipment Master; beyond the comprehension of lower mundane folks like you." Bai Luoran sneered. "Wait, you're from the mundane world? Not from the Cultivation Realm?"
Mo Huasong is from the mundane world, so dealing with him would be easier.
Killing him would entail no consequences.
Mo Huasong nodded slightly, "Yes. This is my last favor to you in your dying moments. You can die now."
With Bai Luoran's magic artifact broken, she could no longer oppose him.