OE

Very experienced performers have so much difficulty with some of Rachmaninoff’s “more perilous [difficult] passages” that it sometimes seems as though the music was intentionally designed to [blank]. The blank must mean something like confuse or cause people to struggle. “Confound” means confuse and so is a good match. “Unnerve,” which means to cause someone to lose confidence, also works. “Transmute” and “transmogrify” both mean to transform, which doesn’t mean difficult. Neither “distribute” nor “malign” (say bad things about or slander) has a match and so cannot be correct.