The mastiff old did not awake,

Yet she an angry moan did make!

And what can ail the mastiff *****?

Never till now she uttered yell

Beneath the eye of Christabel" (Coleridge)

Christabel fails to heed the warning of the mastiff, and so, her fate is sealed. The image of the mastiff is cruel and powerful, and yet, Geraldine's power is even stronger, for she can keep the mastiff still and keep the warning from registering with Christabel. Thus, her evil is powerful indeed, more powerful than the other gothic motifs in the poem.

8. The dead mother is yet another important motif in the poem. She adds to the tragedy of Christabel's life, and Coleridge makes it quite clear Geraldine is far more powerful than a long-dead spirit.

Alas! what ails poor Geraldine?

Why stares she with unsettled eye?

Can she the bodiless dead espy?

And why with hollow voice cries she,

Off, woman, off! this hour is mine

Though thou her guardian spirit be,

Off, woman. off! 'tis given to me'" (Coleridge).

This indicates Geraldine's great power and her influence over the innocent Christabel. The powerful evil temptress is an important gothic element in the poem, and without her, the poem would be dark and brooding, but certainly not as evil and unsettling as it is.

9. In any gothic work, it seems...

"Christabel" is no exception. Her elderly father calls a drafty old castle home, and the images of fires burning, dark rooms, and shadowy stairways almost always occur in gothic works. The elements of the poem are dark and dreary, and so the setting much echo these elements to set the stage for tragedy and evil.
10. Finally, the motif of the dark, "bleak" forest is another gothic element of the poem. The owl screeching, the wind blowing, and Christabel praying for her beloved at midnight all combine into an eerie, unsettling image. Gothic works are dark and sinister, but there is always something "wrong" in them as well. Why is Christabel out alone in the dark woods on such a dreary night? The image is wrong, and yet, it occurs, which is another important element that all lead to a classic and dark gothic poem.

References

Ashton, Rosemary. "The Life of Samuel Taylor Coleridge." University of Alberta. 1996. 15 March 2007. http://www.ualberta.ca/~dmiall/Gothic/Christabel.htm

Coleridge, Samuel Taylor. "Christabel." University of Virginia. 1999. 15 March 2007. http://etext.virginia.edu/stc/Coleridge/poems/Christabel.html

Hogle, Jerrold E. "Christabel' as Gothic: The Abjection of Instability." Manchester University Press. 2005. 15 March 2007. http://journals.mup.man.ac.uk/cgi-bin/pdfdisp//MUPpdf/GOTH/V7I1/070018.pdf