Since reality vs. illusion is a central theme in A Midsummer Night's Dream, the play resembles a masque in that many of the characters are not quite what they seem to be.
Puck is one character that may be more than what he seems to be. On the surface level, we know Puck to be a mischievous and devilish little sprite, as we learn in the second act from Puck's fellow fairy who asks Puck if he is "that shrewd and knavish sprite" (II.i.35). We further learn of his mischievous nature through the descriptions of his antics, such as scaring the "maidens of the villagery" (35). Due to his devilish nature, Oberon believes that Puck has intentionally mixed up the Athenian lovers, making both men pursue the opposite woman, as we see in Oberon's lines, "This is thy negligence. Still thou mistakest, / Or else committ'st thy knaveries wilfully" (III.ii.361-362). However, Puck claims that he made an honest mistake due to the fact that Oberon only told Puck that he was looking for an Athenian man; Puck had no idea there were actually two Athenian men in the forest that night. While it does look like Puck is up to his devilish antics again, we see earlier that Puck felt genuine compassion for the woman he thought was Helena. When Puck finds whom he thinks is the correct couple in the forest sleeping so far apart from each other, he genuinely believes it is because the man hates the lady and is being cruel to her. Since Puck feels genuine compassion for the lady, we know that Puck is only wearing a mask when he acts as a devilish sprite. The reality is that there is more to his character, and he is just as capable of being caring as many other people.
We can also see a mask-like quality in the lovers, especially Lysander. Before Lysander and Hermia enter the woods, Lysander believes that their decision to love and marry is guided by reason. We see Lysander apply reason to argue before Theseus that he is just as worthy to marry Hermia as Demetrius because he is just as high in social status and as wealthy, as we see in his lines, "I am, my lord, as well derived as he, / As well possess'd" (I.i.101-102). Yet, no matter how reasonable Lysander thinks he is, Puck proves through enchantment that Lysander is actually a very irrational being. Suddenly, without any real reasons, Lysander is in love with Helena and believes he hates Hermia. He even still continues to believe that he is being rationally minded, as we see in his lines, "The will of man is by his reason sway'd, / And reason says you are the worthier maid" (II.ii.117-118). Since on the surface level Lysander appears to be a reasonable person, we can say that Lysander is wearing a mask. Lysander's mask presents him as a reasonable person, when in reality he is just as irrational as the rest of mankind.