We especially see Puck portraying the voice of Shakespeare while expressing the themes of human flaws and the irrationality of love. The most prominent place in which the voice of Shakespeare appears through Puck is Act 3, Scene 2 in which both Demetrius and Lysander leave off pursuing Hermia and fall in love with Helena.
Puck finds it very amusing that he mistakenly used the magic flower on Lysander instead of Demetrius, making Lysander fall in love with Helena. He especially finds it amusing and even foolish that Helena, who was pale with love sickness before is now being pursued by a man, and yet she still rejects him. He refers to Lysander's pursuit of Helena and her rejection as a "foolish pageant" and to the characters as "fools" because Helena could have what she wants, which is love, but she is rejecting it, as we see in Puck's lines, "Shall we their fond pageant see? / Lord, what fools these mortals be?" (III.ii.115-116). Puck's opinion clearly states the themes that mankind is foolish and that love is an irrational emotion while also expressing the voice and opinion of Shakespeare.
We further see the voice of Shakespeare in this scene when Puck proclaims the pleasure he is taking from watching the poor four characters muddle through their love problems. In this play, Shakespeare is acting like a puppeteer, making his characters dance about on marionette strings and bend to his own will. Normally, characterization is created in such a way that the character's deepest feelings, like love, remain stagnant. Here, Shakespeare is having his characters' feelings change at the drop of a flower petal. Puck clearly proclaims the fun that Shakespeare is having when he exclaims that having two men fall in love with one woman would be great "sport," as we see in his lines:
Then will two at once woo one.
That must needs be sport alone.
And those things do best please me
That befall preposterously. (119-122)
Having the characters dance about and suddenly change emotions highlights the themes that humans are fools and love is an irrational emotion while also voicing Shakespeare's opinion and showing us how much fun he is having in manipulating his characters.
We further see these themes and the fact that Shakespeare is manipulating the characters through Puck's own declaration that he is manipulating the characters, which is also another clear moment of Shakespeare speaking through Puck, as we see in his lines, "Up and down, up and down, / I will lead them up and down" (412-413). The words "up and down" clearly not only reflect the characters' actions but their changing emotions as well.
In drafting your answer examine the parts of Pucks dialogue where he speaks to the audience, or to himself rather than other characters. These sections are purely for the audeinces benefit. He shows awareness of the audience and adds to the information they possess in a conspiratoral fashion, taking them into his confidence and sharing information that no one else in the plays knows or is aware of. As a representative of the writer, or the authorial voice Puck is aware of this secret information and that the audience needs to know that information as well.
The most obvious section is in his final words:
If we shadows have offended,
Think but this, and all is mended,
That you have but slumbered here
While these visions did appear...
He is aware that none of this is real, it was all a fabrication and a dream, just as the actor is aware that he is acting, and the audience aware that they are watching a play. He is apologising on behalf of the writer in a way, because it is the writers words that made the dream come to life.
A few others to look at:
Lord what fools these mortals be
Cupid is a knavish lad,
Thus to make poor females mad.
Jack shall have Jill;
Nought shall go ill;
The man shall have his mare again, and all shall be well.
Now the hungry lion roars,
And the wolf behowls the moon;
Whilst the heavy ploughman snores,
All with weary task fordone.