Frightful must it be
This sudden elevation of language should not be merely dismissed as a facile rhetorical heightening for effect. What Mary Shelley seems deliberately to be doing here is evoking a succession of elements and emotional states associated with the Sublime in eighteenth-century aesthetic theory. As the Creature in his coming to life is associated with the Sublime, so he is its avatar wherever he appears in the novel, either living within a sublime landscape (e.g. Mont Blanc or northern Siberia) or terrifying the human beings whom he encounters by his extra-human size and countenance.