Puck, also known as Robin Goodfellow, is a trickster nature sprite or fairy who is a servant and jester of the court of Oberon. The Welsh called him Pwca, which is pronounced the same as his Irish incarnation Phouka, Pooka or Puca.
As a shapeshifter, Puck has had many appearances over the years. He's been in the form of animals, like how the Phouka can become a horse, eagle or donkey. He is also depicted as a rough, hairy creature in many versions. Puck used his shapeshifting to make mischief. For example, the Phouka would turn into a horse and lead people on a wild ride, sometimes dumping them in water. The Welsh Pwca would lead travelers with a lantern and then blow it out when they were at the edge of a cliff.
He first appears in the play A Midsummer Night's Dream. The character himself is based on older English mythology about a sprite who would cause travelers to lose their way at night with sounds and lights. For the last thousand years, he has been known as a faerie, sprite, goblin, devil or imp.
When Aleph arrives to the Yousei Kingdom ruled by Oberon, they encounter Puck who tries to throw the infidelily sap at Aleph but Hiroko gets hit with it, which makes her fall in love with the first person she sees. Oberon tells Aleph that he needs a sample of infidelily sap in order to undo the spell. Aleph later encounters Puck in a dungeon where he surrenders to Aleph. Here Aleph makes an alignment choice. Puck offers Aleph the sap for 10,000 macca. If Aleph accepts, he becomes more lawful. If he refuses, Puck will give the sap for free, which is a neutral choice. Aleph can refuse this offer, causing Puck to offer 10,000 macca as compensation for the trouble he caused. If Aleph becomes greedy and threatens Puck again, Puck will run away, dropping the sap but paying no money. The last two are chaotic choices.
Persona 2: Innocent Sin
Puck is first encountered in Kasugayama High when the party goes to investigate the student council president.