Answer and Explanation:
Mark twain presents the serious and sad moments in this story in a playful, ironic and demonstrating way that the result of these terrible moments led to situations so surreal that he could only find grace in them and mock them with much sarcasm.
Sarcasm is primarily responsible for Twain's humor in this work and can be seen at various times, even when he irks a man's motto, as can be seen in the paragraph below:
"Presently, when things began to look dismal again, a desperado killed a man in a saloon and joy returned once more. I never was so glad over any mere trifle before in my life. "