Gort is a banshee, an evil pixie that needs to consume the soul of a human being, every seven years to survive. In order to do this, he must make a human being drink a potion called "The Glamor" and recite a specific verse :"Turn me now into spirit bright and leave behind the human plight". The victim has to do this multiple times, for it to fully take effect.
Then soon enough after saying the oath and drinking the glamor many times, the victim is transformed into a small helpless creature, one that somewhat resembles a frog. This is known as a changeling, the banshee is in complete control of it for the next seven years, slowly feeding off the small helpless creatures soul.
A short time before the events of the episode, Gort had a conflict with a Leprechaun named Sean O'Shaney who cut off his tail after one of their conflicts. The two of them were sworn enemies with nothing but pure hatred and animosity for each other.
Gort soon moved from Ireland to Canada, where he found himself a new identity, going by the alias of Erin and living as
a stage actor. In his human form, he was very friendly, jolly and admired by everyone, especially Jake Joysen, a young boy who dreamed of being an actor and admired him for his ingenious skills and talented acting.
Gort picked Jake to be the lead in his play he called "Will O' the Wisp", the play was about a young boy being terrorized by an evil goblin. The boy is then rescued by a Leprechaun named Seamus Doyle, who turns the boy into a Leprechaun to protect him from the goblin. Gort himself portrayed Seamus Doyle. Which in reality, he was a villain posing as hero in his own fictional play.
But underneath his friendly and pleasant exterior, Gort planned a poor and cruel fate for Jake. Using Jake's hat and a photograph of the boy, he erected a shrine in his dressing room where he had cast spells to take and consume the boys soul. In the play in order for Jake's character to become a leprechaun, first Seamus would instruct the boy to dance around and recite the verse: "Fairy Rings, Dance and Sing, The Mortal Gloom a Dying Thing". Then the boy was tossed a pouch, and was instructed to drink from it. Then the boy would be instructed to say: "Turn me now into spirit bright and leave behind the human plight". By being instructed by him to do this, the boy would be transformed into a leprechaun and be able to escape from the goblin.
What Jake didn't know was that the "Glamor" was actually the potion, that was slowly turning him into a changeling, so Gort could steal his soul. Every time he took the oath,he changed a little bit more. As for opening night, he'd take the oath for the final time and change completely. Gort was planning for the audience to think Jake's transformation into a changeling was just part of the play.
A fearful Jake sought assistance from Sean O'Shaney, who owned a greenhouse nearby. Sean was able to figure out Erin's true identity. Because Jake was interested in the tea he drank, which made apparently helped him with his acting. The ingredients were Bluebells, Foxgloves and Ragweed. The only creatures who seek these herbs for tea, are evil pixies and banshees, which hinted to Sean who Erin actually was. Therefore Sean began secretly helping Jake overcome him by giving him potions and bugs to swallow to make him fearless.
On the night of the performance, everything went normal until it was time for Jake's character to say the oath and drink the glamor. He said the oath, but didn't drink from the pouch. Instead, Jake smirked at him and threw it back to him. This made him mad, realizing he'd been talking to someone behind his back.
After Jake lost his gaze on him, Gort, transformed into his actual banshee self and went after Jake on stage. Then just as he had hoped, the audience just thought it was part of the play. When Sean arrived the roles were now somewhat reversed, now Gort was the villain and Sean was the Leprechaun. It seemed that he had placed enough glamor into Jake's system anyway, and Jake became a changeling and he claimed him to be his and was about to take off with him.
Then Sean presented his tail to him saying he had kept as a souvenir for many years, Gort was shocked and demanded it back. Therefore Sean offered to trade him, his tail in return for Jake's soul. Since a Banshee is a type of pixie, when they're offered a trade, they can't refuse it no matter what they'll be given in exchange. That is as long as they tell them the proper incantation. Gort was compelled to agree, when Sean yelled the incantation to him: "yours be mine, and mine me be yours". He then threw his tail back to him, then he suddenly vanished in a flash of bright light and he was never seen again.