The supernatural pertains to anything out of the ordinary. It can relate to ghosts, fairies, magic, even anything divine. There are many elements of the supernatural found in A Midsummer Night's Dream. One of those elements is the fairies, or more specifically, Puck. One of Puck's roles as the supernatural is to portray one of Shakespeare's most critical themes in the play, that mankind is foolish.
It is ironic that Puck helps to elaborate on the theme of the foolishness of men as Puck is one of Shakespeare's fools in the play, alongside Bottom. However, Puck is a fool in the traditional sense that he serves as a fool, or a court jester, to King Oberon, as we see in his lines, "I jest to Oberon, and make him smile" (II.i.45). Puck, like one of Shakespeare's traditional fools, is amusing and quick witted, even proclaiming many astute observations. Bottom, in contrast, while he does say one thing enlightening, is generally ridiculous, causing all sorts of problems with his ridiculousness. Puck portrays the theme of man's foolishness by literally making a proverbial "ass" of his fellow fool, Bottom.
Puck, as one of the elements of the supernatural, portrays the theme of the foolishness of men by turning Bottom into a donkey, using magic. A slang term for a donkey is an "ass," which is also a slang term used to describe a particularly conceited, stubborn, and foolish person. Hence, by turning Bottom into a donkey, Puck is commenting on Bottom's foolishness. We especially see Puck commenting on Bottom's foolishness in his line, "A stranger Pyramus than e'er play'd here!," which is a direct reference to just how poorly Bottom is rehearsing his part as Pyramus, despite Bottom's earlier confidence (III.i.81). Aside from turning Bottom into a donkey, we further see Puck relaying the theme of men's foolishness when he comments on the foolishness of the Athenians, as we see in Puck's famous line, "Lord, what fools these mortals be!" (III.ii.116).
Hence, we see that Puck's role as an element of the supernatural is to relay the theme of the foolishness of mankind. We also see that one purpose of the supernatural in general is to relay critical themes.