Oberon tells a story about how he discovered the magic juice and how it was created: One time, when he was watching a mermaid riding around and singing on a dolphin's back, he noticed that Cupid was trying to hit a virgin queen with his love dart. Cupid missed his mark and hit a white pansy instead, turning it purple and giving it magical properties. 
 Oberon tells us that he plans to sprinkle the love "juice" in Titania's eyes while she sleeps. When she wakes up, she'll fall in love with the first thing she sees. While Titania's busy being in love, he'll take the boy from her.

Oberon watches as Demetrius mistreats Helena. He decides Demetrius needs a little dose of the love juice as well.

Oberon tells Puck to sprinkle the potion in the "Athenian man's" eyes so he'll wake up and fall for Helena. Oberon doses Titania with the juice while she sleeps.

4- Oberon learns that Titania woke up and immediately fell in love with an "ass" (Bottom). 

Oberon learns that Puck screwed up and put the love potion in the wrong Athenian man's eyes and now Lysander loves Helena. 

Oberon tries to fix things, so he sprinkles the potion in Demetrius's eyes so he'll fall for Helena.

Oberon watches the young Athenian men fight over Helena in the wood. Eventually, he tells Puck to fix it so that Lysander will love Hermia and Demetrius will love Helena. 

Oberon watches Titania as she sleeps, curled up next to her new lover, Bottom. He says that he feels bad that he made his wife fall in love with an ass.

Oberon is very satisfied and decides to reverse his wife's love spell. He also orders Puck to fix Bottom's head.
Oberon takes Titania in his arms and celebrates being together once again. He tells her that tomorrow they'll dance in the Duke's house in Athens, blessing it and all the couples merrily.