Oberon, traditionally associated with order in A Midsummer Night's Dream, causes chaotic activity in this act. He has given Puck instructions to anoint the youth wearing "the Athenian garment"; however, Puck mistakenly anoints the eyes of Lysander with the love portion, instead of those of Demetrius. When Lysander opens his eyes, then, he falls in love with Helen who has awakened him after entering the woods in pursuit of Demetrius. With the potion on his eyes, Lysander falls in love with Helen, but she believes that he mocks her as he speaks of his regret about loving Hermia.
When Lysander does see Hermia, he no longer loves her; he loathes her. The arguing of Oberon and Titania has caused the natural world to be at odds with itself. In his efforts to control Titania and bring peace to his marriage, which will effect a settling down of Nature, Puck's mistake causes more unrest.
Oberon plans to take the changeling child of Titania while she is under the spell of love. However, Oberon is unaware that Bottom has entered the forest to practice a play with the other mechanicals. An observer of their bungled practice is Puck, who turns Bottom's head into the head of an ass. After this trick, Titania awakens, and looks first at Bottom, falling in love with the man who has the donkey's head.
What follows is hilarious as Bottom, unaware of his changed head, he accepts his position as lover to the fairy queen when she tells him "I love thee":
methinks, mistress, you should have little reason
for that; and yet, to say the truth, reason and love keep
little company together now-a-days; the more the pity,
that some hones neighbours will not make them friends.
Nay, I can gleek upon occasion. (3.1.134)
Bottom banters with the other fairies, a comical scene, indeed, as a man whose head looks like that of a donkey criticizes others.