"You can just make more children after all".
"And this is a 1-hit sure kill fighting spirit fencing arts* technique from the East."
"Evil god rending fencing arts* ultimate technique." (*also in both cases not sure if "arts" is necessary, or whether it should be "art", "martial art" or simply "fencing technique" since it being a martial art is implied in context).
"You should always keep your ace up your sleeve until the end..."
"I have something to discuss with Mr. Boss Bear." ("some things" is technically also correct, but we see in the next chapter that it's just one thing: leaving the forest).
That's all I noticed as far as grammatical errors are concerned. But there could be more since I'm not a native speaker.