Astonisher

(colloquial)

Source: wiktionary

[…] the railroad between Leghorn and Pisa […] has already begun to astonish Italy with a precedent of punctuality, order, plain dealing, and improvement—the most dangerous and heretical astonisher of all.

Source: wiktionary

1858, Abraham Lincoln, debate with Stephen A. Douglas on 10 July, 1858 in Speeches and Letters of Abraham Lincoln, 1832-1865, London: J.M. Dent and New York: Dutton, 1907, p. 88, It [this court decision] is the first of its kind; it is an astonisher in legal history; it is a new wonder of the world;

Source: wiktionary

He [the king pretending to be a peasant] was always frightening me, always breaking out with fresh astonishers, in new and unexpected places.

Source: wiktionary