Bizarrely, when Halloween II came out, Michael Myers looked totally different -- which was especially odd because the events of the movie kick off literally moments after the original ended. The pristine white visage was suddenly discolored and worn, less Star Trek William Shatner and more Priceline.com William Shatner.
It turns out that this was the exact same mask from the first movie. But it looks totally different for a few reasons. For one, Michael was played by an entirely different actor who didn't go on to write Hook, the improbably named stuntman Dick Warlock. Secondly, no one seemed to give a crap about preserving this mask. The original actor, Nick Castle, shoved the mask in his pockets while making the first movie, and before the sequel went into production, the mask was stored not in some fancy studio vault, but under the bed of a producer, whose smoking caused it to "rot and yellow."