In a speech which echos a bit of the prologue to "Pyramis and Thisbe" within the play (which runs amok due to misplaced punctuation), and which picks up on Theseus's comments that the best actors are shadows. It also presages lines in Act V, scene 5 of a certain "Scottish" play written by Shakespeare nearly a decade later, in which Macbeth says "Life's but a walking shadow, a poor player/That struts and frets his hour upon the stage/And then is heard no more: it is a tale/Told by an idiot, full of sound and fury,/Signifying nothing."
Puck, one of the names of Robin Goodfellow, closes the play as follows:
If we shadows have offended,
Think but this, and all is mended,
That you have but slumber'd here
While these visions did appear.
And this weak and idle theme,
No more yielding but a dream,
Gentles, do not reprehend:
if you pardon, we will mend:
And, as I am an honest Puck,
If we have unearnèd luck
Now to 'scape the serpent's tongue,
We will make amends ere long;
Else the Puck a liar call;
So, good night unto you all.
Give me your hands, if we be friends,
And Robin shall restore amends.
I tried to find Robert Sean Leonard's performance in the version of the play nested inside The Dead Poets' Society, but to no avail. Instead, you can watch Stanley Tucci, starting at about 3:42 in this version: