And some in dreams assured were
Of the spirit that plagued us so;
Nine fathom deep he had followed us
From the land of mist and snow. (II.31-32)
Weird stuff starts to happen after the boat has been sitting idly on the water for a while. The water is filled with colors that witches might produce in their potions, and the crew members start dreaming about a supernatural "spirit" that lives deep under the ocean but which now haunts their ship. There are quite a few different supernatural elements to keep track of in this poem.
Alas! (thought I, and my heart beat loud)
How fast she nears and nears!
Are those her sails that glance in the sun,
Like restless gossameres?
Are those her ribs through which the sun
Did peer, as through a grate?
And is that woman all her crew?
Is that a Death? and are there two?
The arrival of Death and Life-in-Death is a symbolic event described as a supernatural one. A ship would not normally travel with tattered sails and a skeleton-like hull, but we're not in "normal" territory, either. How does the Mariner identify Death and his mate so quickly?
'Still as a slave before his lord,
The ocean hath no blast;
His great bright eye most silently
Up to the moon is cast –
If he may know which way to go;
For she guides him smooth or grim.
See, brother, see! how graciously
She looketh down on him.' (VI.94-95)
This quote is taken from the conversation of the two voices in Part VI. The second voice explains that the ocean doesn't really have its own free will; it does whatever the moon wants. And who is the moon? We're not sure, but she might be associated with the Virgin Mary or another religious figure. The moon is personified as a female, as in most classical mythology. She doesn't stay mad forever and is capable of showing pity toward the Mariner.