What are the supernatural elements in "The Eve of Saint Agnes"?

Supernatural elements abound in John Keats’s poem. "The Eve of St. Agnes" centers on a girl, Madeleine, who dreams of her desired lover, Porphyro. He enters her bedroom and looks at her while she dreams, and then when she awakens, they flee together. Two large questions remain, however—whether the whole poem is a myth or folktale, and this event never happened; and, if it is an actual event, if the girl is dreaming the lover and their escape. The use of multiple references to supernatural states, such as enchantment and spells, and beings, such as faeries and dragons, exaggerates the mysterious effect.
The old man who admits Porphyro recommends he safeguard himself with supernatural means: “Thou must hold water in a witch's sieve, / And be liege-lord of all the Elves and Fays.” “Fay” here is another word for “fairy.”
While Porphyro enters Madeleine’s room and watches her, he sees fairies on her coverlet and that

pale enchantment held her sleepy-ey'd....
'twas a midnight charm....
It seem'd he never, never could redeem
From such a stedfast spell his lady's eyes.

He mentions the legendary sorcerer Merlin, who fought a Demon. Then, rather than just watching her, Porphyro joins into that enchanted state: “Into her dream he melted, as the rose / Blendeth its odour with the violet." When she wakes up, Madeleine sees him but wonders if she is still dreaming, saying he looks “immortal” more than human. She frets that he will leave her.
After they flee the palace, which is guarded by dragons, the narrative switches away from them and emphasizes that these events happened “ages long ago.” The poem states that “These lovers fled away into the storm,” but earlier, Porphyro had called it “an elfin-storm from faery land,” implying that the whole episode may be unreal.
Finally, the action switches to the Baron who lives in the palace, who “dreamt of many a woe.” Not only he but his guests have long nightmares featuring images “Of witch, and demon, and large coffin-worm.” These associations with the supernatural and death further suggest that the story does not depict a dream or fabulous tale rather than real events.
http://academic.brooklyn.cuny.edu/english/melani/cs6/st_agnes.html

https://www.poetryfoundation.org/poems/44470/the-eve-of-st-agnes