I did the SFX for that show at Rugby Theatre a couple of years ago; here are the four main effects we used:
The script calls for Scrooge to see his door knocker turn into Marley's face. I did this with a rubber sheet and vacuum. There was a vacuum chamber (a deep turkey-roasting tray) set into the door, with a plaster sculpture of a face fixed inside. The thin rubber sheet was stretched over the rim of the tray, and normally was flat so it just about touched the nose of the face. By sucking the air out on cue, the rubber contoured itself around the face and the inside of the tray, and at the same time a spot illuminated it from the front/side. We had to forego the knocker, and instead just got the face appearing in a plain black door panel.
I couldn't find a commercial source of thin black stretchy rubber sheet (a bit thicker than a toy balloon), so I had to make my own. I did that by mixing a little indian ink into some latex solution (beware other colouring agents, like poster paint, will coagulate it), and painted about six coats onto a flat metal sheet, with talcum powder applied afterwards to prevent it sticking to itself. With a big enough tank of latex, dipping in a plate would be easier, but that wasn't practical for a one-off.
To get the air out quickly and quietly, I rigged up a vacuum reservoir (actually a 5-gallon compressed air receiver, but a beer-brewing pressure barrel or something would do). Before the show ran a vacuum pump to remove some of the air, down to a predetermined pressure, then sealed it off. On cue, I opened a valve to let the reservoir and roasting tray equalise in pressure (via a 1/2-inch plastic tube that led out through the door hinge), then pulled the tube off the pipe from the valve to let air back in again.
I've since read about a similar effect used in Disneyland, in which a cartoon character springs out of a TV screen. In that case, the sculpture is thrust through the rubber screen at the same time as applying vacuum, with coordinated lighting and (I think) film projection. Nice stuff if you have the budget for computer-controlled hydraulics etc.
When Scrooge is in his bedroom, we had the first Ghost appear suddenly through his closed bedroom door, by having an empty doorframe covered in two overlapping black Lycra sheets so he could push through the vertical slit. This was not particularly successful, I must admit, and relied on dim lighting to hide the details. There was a removable sheet of hardboard over the back of the door, so Scrooge could use the door without the Lycra flapping in the breeze.
Obviously this is a potentially dangerous effect; I ensured everything on stage was thoroughly fireproofed, and was always watching it in action with a fire extinguisher nearby. I somehow convinced our safety officer that it was OK.I would have preferred a whiter flame personally, like on Nichol Williamson's (Merlin's) magic staff in the film Excalibur, but I think you need acetylene for that - much more tricky.
For the Ghost of Christmas Yet to Come, we opened the doors we have in the back wall of the stage, and built a tunnel extending into the yard outside. The Ghost could then be seen to approach from a distance, with a 2 kW lantern behind him gelled in red with a break-up gobo, projecting beams of light through smoke into the audience.
I hope that's inspired you somewhat; I guess some brainstorming among your production team could come up with more ideas.
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