I'm not sure if you remember but there was a song out in the 80's called "Close My Eyes Forever" that was a duet by Ozzy Osbourne and Lita Ford. A couple years ago, someone called a local rock station to request it (they often play callers on the air) and said "I want to hear Close My Eyes Forever by Ozzy Osbourne and Lena Horne."
Needless to say the DJ laughed for like 10 minutes on air.
back to the question, I also think it should be an unknown or slightly known with an outstanding voice. Dubbing ain't gonna cut it.
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