What is the mood of the story? what phrases create the mood?

I think that overall, the mood of this story is dark, foreboding, and surreal. This links into many of the themes of the story. The supernatural lends itself well to the dark rather creepy mood. There is a sense that perhaps the power of the Monkey's paw is not benevolent. The old motif of being wary of one wishes for is at play here. There are other themes which incorporate nicely with the theme of the "supernatural". Fate and free will, death, and culture can be considered as well,

"He found the monkey’s paw, and frantically breathed his third and last wish. The knocking ceased suddenly . . . a long loud wail of disappointment and misery from his wife gave him courage to run down to her side..."