Hyperbole

Deliberate exaggeration, which no one takes literally, used to give emphasis to a feeling or a situation.

In Demons

The most repulsive and the most frightening that could possibly be.

The double superlative, "the most repulsive and the most frightening that could possibly be," pushes Nikolai's anger to the limit of the imaginable. The exaggeration makes the reader feel that his self-control frightens more than any explosion would.

Part One: The Slap, the chronicler, on Stavrogin's anger

The mystery of the appearance of a new being, a great mystery, inexplicable, Arina Prokhorovna, and what a pity that you do not understand it! [...] There were two, and suddenly a third being, a new spirit, whole and complete, as does not come from human hands; a new thought and a new love, it is even frightening... And there is nothing higher in the world!

Part Three: The Last Decision, Shatov