Haunted Mansion has always been known to have several gags throughout the attraction and even in line.  A long time easter egg has been the tombstones that appear throughout the queue.  The headstones had references to the Imagineers that worked on the ride.  According to the original post on Disney Parks Blog, they were removed at the start of Haunted Mansion Holiday, but not found again to be put back.  Instead, new tombstones were made with the same labeling as before.  Also new tombstones were created with recent Imagineers that have worked on the attraction.  They are all found up on the hill behind a wall in the queue.  Right now the hill also features pumpkins for Haunted Mansion Holiday.