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This is a new word for me. It functions as an intensifier, like the dickens, tarnation, Hell.

You can find an entry for flugens in The Dictionary of American Regional English (vol. 2); Frederic G. Cassidy, Joan Houston Hall (eds.); 1991; the President and Fellows of Harvard University.
flugens

Also flugins, flujens, flujin, flugence, fluzions
cheifly Southern
The earliest example shown in the entry above dates to 1830, and the most recent is 1954. One of the 1954 references mentions that it is "not common, but still heard."