This is the 13211th most frequent Russian word.
мистическими
"Mystical" or "mystic" (instrumental plural form).
The adjective "мистическими" describes the characteristics or qualities of the elements in the novel.
Этот роман наполнен мистическими элементами.
This novel is filled with mystical elements.
Here, "мистическими" modifies "практиками," referring to practices that relate to mysticism or spirituality.
Они увлекались мистическими практиками в поисках истины.
They engaged in mystical practices in search of truth.
In this sentence, "мистическими" describes the powers, indicating their mysterious or supernatural nature.