Tim is right. The word only has three syllables; there's no second I. Its MISS-chə-vəs or MISS-chə-vuss. I've never heard the accent on the phantom fourth syllable that Oli describes. Perhaps it is just a UK thing. It's nice to know that my people don't have a monopoly on stoopid pronunciations. I think they're reading it dyslexically as "mischevious" or, in the pronunciation Oli describes, "mischiveous."