I was driving home the other day and Night on Bald Mountain was on the radio, but it wasn't really Night on Bald Mountain. There was a vocal component to it that I had never heard before, and I ended up listening to the entire thing. It turns out that this was an earlier version of the work, called St. John's Night on the Bare Mountain. Confused, I looked the work up when I got home.
Mussorgsky's personal life was apparently something of a mess -- and by that, I mean, he was an absolute wreck. So much so that when he died young, he left behind piles of manuscripts in various states of completion and/or disrepair, which is why the most famous version of Night on Bald Mountain, the one that everyone knows, is actually an edit made by Nikolai Rimsky-Korsakov. (Also, his famous Pictures at an Exhibition's orchestral version is by Maurice Ravel.) At some point, Mussorgsky made a version including child choir, standard choir, and baritone soloist. It's hard to figure out what is Mussorgsky and what belongs to later editors, but this version of the work is, to my ears, more interesting than the standard Rimsky-Korsakov arrangement.
And as a bonus, here's another Halloween-appropriate work, Rachmaninov's Isle of the Dead.