Frank Norris, The Octopus: A Story of California, 1901 Another sense of wicked means "of exceptional quality or degree." It often carries the insinuation of being so impressive or incredible as to confound: The Mud Hens had a roster slot, and the scout had a notion to fill it with the pitcher with the wicked curveball, name of Earl Grayson.
The hero calls in Gridley Quayle, and that patronizing ass, by the aid of a series of wicked coincidences, solves the mystery; and there am I, with another month's work done." P.
In that part of the country in particular, wicked is commonly recognized as its own intensifying adverb meaning "to an extreme or impressive degree": "It's wicked competitive," said Massachusetts Gov.
1997 The folks at the Sportsman's Alliance of Maine (SAM) and the Maine Snowmobile Association have gotten wicked worked up about a wrinkle in the deal by the state to acquire the spectacular lands around Katahdin Lake and attach them to Baxter Park.
Smith of Dialect Blog notes, the use of wicked as an adverb echoes the similar use of other adjectives, such as awful and terrible (e.g., "a terrible cold frost"), as intensifying adverbs that saw use as late as the 19th century.