If you have /watch on and the Halloween 2012 maps play, mice that are touched by ghosts and/or skeletons won't be transparent.

[example in case my description skills need work]
so, say that you have only yourself watched. the halloween 2012 maps begin to play. souris1 is touched by a ghost, which makes them a reddish color. after the reddish color stops, souris1 will show up normally, instead of transparently.

excuse the lack of graphics and stuff.