Final answer:
The figurative language in the quote is identified as hyperbole, which is an exaggeration used for emphasis.
Step-by-step explanation:
The figurative language used in the quote "...and some that smile have in their hearts, I fear, millions of mischiefs" can be identified as a hyperbole. A hyperbole is a figure of speech that involves an exaggeration of ideas for the sake of emphasis. It's not meant to be taken literally as it is simply an overstatement to stress the point. The phrase "millions of mischiefs" exaggerates the amount of ill intent within someone who is outwardly smiling, which effectively communicates the contrast between their appearance and their true feelings or intentions.