What happens when Haroun drinks the stoty water Iff gives him?

Iff dips into the Ocean and produces a golden cup with a story inside. Haroun drinks the water and finds himself looking through the eyes of a young hero in a land full of monsters and strange things. There is a princess in a tower and Haroun watches as the hero dispenses with the monsters and begins to climb the tower. Halfway up the tower, the hero begins to turn into a spider and when he reaches the top, the princes begins to hack away at the horrible creature until the hero falls to the ground.