In Act 3, sc 2, Puck reports on Titania's ludicrous infatuation, to Oberon's delight. Demetrius and Hermia appear, arguing. She leaves angrily, and Demetrius, worn out, falls asleep. Oberon realizes that the wrong man has been treated with the magic juice. He commands Puck to lure Helena, which he himself charms Demetrius with the herb. When Helena arrives, Lysander follows, pleading his love. Demetrius wakes; he falls in love with Helena adn begins to praise her beauty. She concludes the two men are mocking her, and she rebukes them. Hermia enters in search of Lysander. She is bewildered at Lysander's behavior. Helena is insulted and concludes that Hermia is in on the joke with the two men since she thinks Hermia is belittling her. After a series of exchanges, during which first the men and then the women almost come to blows, the men leave to fight a duel. Helena flees Hermia's wrath, and Hermia leaves baffled. Oberon directs Puck to summon a dense fog and then to impersonate each man to the other and lead them away from one another and conflict. Then he is to apply the antidote to Lysander's eyes. Puck leads the men on separate chases until each falls exhausted on opposite sides of the stage. Helena and Hermia also sleep. Puck squeezes the juice on Lysander's eyes and sings a song of reconciliation.
Oberon likes to play jokes, but he also cares about the people enough to fix it.
Oberon is happy to hear from Robin that Titania has fallen in love with Bottom who now bears an ass's head instead of his own - "This falls out better than I could devise." His plan worked. This tells us that he is mischievous and a bit vengeful because he had Puck put the nectar on Titania's eyes so that'd she'd fall in love with the first person she spied upon waking as a means of distracting her so that he could get the changeling from her. He wanted the changeling because he was jealous that she was spending so much time and attention with this child and not with him. Also, in this scene, we see that Oberon is a romantic. He had previously witnessed Demetrius' rebuff of Helena and her declaration of love for him, so Oberon asked Puck to annoint Demetrius' eyes so that he'd fall in love with Helena. When Oberon realizes Puck erred and annointed Lysander's eyes, Oberon has the situation rectified so that Demetrius loves Helena and Lysander is back in love with Hermia. All are happy and in love.