The answer is: D. Metaphor
When Poe refer to the mimes as “puppets” in doing a comparison, now we need to determinate if it is either a simile or metaphor, both are figure of speech used to contrast one object or person to another, the difference is that the simile use the word like or as to compare the object or person and the metaphor directly state the comparison. Here is the excerpt from "The Conqueror Worm" where the puppets are mention in the poem.
“And hither and thither fly—
Mere puppets they, who come and go
At bidding of vast formless things”
He never uses the words like or as he does a direct comparison or metaphor.