Puck talks with another fairy about the troubles of Oberon and Titania, king and queen of the fairies. The other fairy describes Puck as mischievous: He frightens the maidens of the village among other things. Oberon resents Titania's having a changeling and orders her to relinquish it; however, she refuses. So, Oberon enlists Puck to find a flower that makes people fall in love. Meanwhile, Oberon learns of the problems that the mortals are having--a young woman has been jilted--and instructs Puck to place the love juice on the eyes of Demetrius. But, Puck mistakes Lysander, who has eloped with Hermia, for Demetrius. When Helena comes in search of Demetrius, Lysander wakes and falls in love with her. Oberon tries to correct things by anointing the eyes of Demetrius, who wakes and falls in love with Helena. Hermia arrives and accuses Helena of stealing her lover. Puck is delighted at the chaos: "What fools these mortals be."
While the craftsmen prepare for a play, Puck changes Bottom's head to that of a donkey and has great fun watching as Tatiana falls in love with him when she awakens. Finally, Oberon, who has taken the changeling, orders Puck to return Bottom to himself and make the lovers fall asleep and reanoint them to correct the mismatches.
While Puck carries his mischief a little too far, he does apologize at the end of the play, contending that it is all but a "dream."
Most Elizabethan audiences would have already been familiar with the names "Puck" and "Robin Goodfellow", as this character had been around since 1531. A "puck" was generally thought of to be a pagan trickster or woodland sprite who led people astray with false echoes or lights, or played practical jokes like souring the milk in a churn. The word "puck" or a variation can be found in the folktales of many countries in Europe. "Robin" is sometimes compared to "hobgoblin", a similar type of mischievous spirit.
What is he doing? The first line references "frightening maids", which is pretty self-explanatory, and "skimming milk", which would be souring it. The wife churns "bootless" meaning no butter will form, and the "barm" (yeast) is gone from the drink so it no longer makes beer. The "quern" refers to a hand mill.
Good or bad seemed to depend on your relationship with him, since if you could get a puck's favor, he would do simple household chores for you, like mending. In Shakespeare's case, the text seems to show Puck as simply a merry trickster who adds charm and humor to the tale. Shakespeare makes this point of view clear with Puck's monologue at the end of the play.