Ever wonder how Disney managed to create real see-through animatronics for the Haunted Mansion attraction? Most of the special effects in that ghoulishly delightful attraction were pulled off using old vaudeville illusions.
In the case of the translucent specters, Imagineers turned to a classic magic trick known as Pepper’s Ghost. A giant pane of glass is placed between the audience and the stage. A light is shined on an unseen object (for example, an animatronic). And if the angle is set just right, a translucent reflection of said object should be clearly visible to your astounded object.
The largest current usage of the Pepper’s Ghost illusion is in fact in the ballroom of the Haunted Mansion, where a pane of glass 90 feet long and 30 tall separates your Doom Buggy from the reflection of over 12 animatronics hidden in a secret room beneath the track on which you travel.
Growing up in Los Angeles in the 70s/80s we visited Disneyland on a regular basis and often after school, before "Annual Passes".