My brother (MIBRO) enlisted my help to make a creepy figure appear to play the organ.  He originally had planned to make a PVC torso rocked back and forth by a windshield wiper motor, powered by an adjustable power supply on a timer. The power supply was an AC-to-DC converter and the timer one of those that turns the mains current on and off.

After discussing the parameters of the project, we decided to purchase a sound player that could be loaded with a sound file and play it when a button was pressed. The button would then be replaced by a relay that would close when the power came on to move the torso. We settled on this sound player. It was not the least expensive but had decent ratings.

Note how everything is taped to a large sticker with double-sided foam tape. This is important later.

MIBRO came by to deliver the sound module to me for modification. While visiting me at A Certain Place, I pointed out a Dancing Skeleton decoration. This hideous little skeleton had bulging glowing blue eyes and arms that would wave up and down on alternate sides while it sang about ghouls dancing about like fools. The arms were quite poseable. This video (not mine) illustrates the action of the Dancing Skeleton (SKELLY). SKELLY is activated either by a DEMO button or by a sound sensor. More on this later. 

Above, the skeleton animatronic (SKELLY) in its natural habitat.

The motion was perfect and it was half the price of the windshield wiper motor with power supply. MIBRO purchased it immediately.