On Thursday, 26 July 2018 10:59:06 UTC+1, Bert Coules wrote:
Any thoughts on how to construct the dummy figure? A lightweight head and
shoulders which support the robes, suspended and released from above?

Possibly, and if you use an electromagnet inside the head and a small black steel plate suspended on a black wire you can release it from ground level without any strings flailing about (or, indeed, give it a DMX relay and release it from the lighting desk).

An inflatable figure punctured with a pin (and presumably
patched up each night for the next show)?

An inflatable figure with a hose attached, and it can be inflated and deflated quite rapidly with a pump. Has the advantage the figure only has to be attached to anything with a small hose, and can be placed into position and moved about without having to attach to a suspension. Deflation won't be instantaneous though, and there may be some air or pump noise. Deflating inflatable dolls may be too reminiscent of Only Fools and Horses, though.

If you haven't found it already the Blue Room Forum has people knowledgeable about such things (and may already have one available for hire or loan).

For some reason I'm thinking car electric aerial mechanisms and bowden cables.

Owain