If the hero has won their ultimate boon by force, if they have stolen it from an angry or jealous deity or protector, they must escape them during the magic flight. If the hero has been granted their boon from a benevolent god, this step in the monomyth is not always present.
Professor Joseph Campbell: "...if the trophy has been attained against the opposition of its guardian, or if the hero's wish to return to the world has been resented by the gods or demons, then the last stage of the mythological round becomes a lively, often comical, pursuit. This flight may be complicated by marvels of magical obstruction and evasion."
If the hero has forcefully taken their prize, they are often chased by some sort of seemingly supernatural being. This being represents the concepts of death and duality that threaten to overwhelm the newly enlightened hero's new state of mastery. In fleeing this creature, the hero is fleeing those old ideas about eternity that no longer serve them yet may continue to linger or refuse to go away after higher consciousness has been achieved.
The obstacles that stand in the hero's way during the magic flight are different than those they encountered along the road of trials, as those all dealt with the hero's Self. The obstacles in the magic flight instead deal with the hero's ideas of the Universal. The signify the long-held ideas about death that the hero must banish from their own minds. so that they may actually experience death for what it is, not what they had been taught it to be.
From a storytelling point of view, the magic flight is often one of the most thrilling parts of a myth for audiences. The hero has already won their prize, and the audience knows that everything rests on their final escape, their mad dash back to safety. The hero almost always succeeds in their magic flight, and so any anxiety the audience feels regarding their safety is abated by the certainty of the hero's success and the fact that they have already accomplished that which they set out to do.
The magic flight continues in the same fluid, dream-like place as the ultimate boon and the refusal of the call. It is the place between places, the eternal now. The only real monster here can be the reflection of the hero, their former self refusing to let them continue as their newly realized self. Before they can cross the threshold back into their old way of life, they must shed forever the ideas that had made them unsatisfied with their state in the first place, that made them heed the call to life-changing adventure.