Production made and sold in auction by Screenused (see original listing here), this amazing prototype SFX General Klytus mask with interior skull was made for Peter Wyngarde’s gruesome/hilarious death scene.
A somewhat raw cast having been filled/sanded but abandoned before the iconic gold plating could be applied, the key identifier for its intended use is the fixed position of the lower jaw to allow the SFX tongue to poke through.
According to the notes on the Screenused listing, the alien-looking skull was apparently created for an alternative ending but offers no further details. Interestingly both the alien skull and what could very well be this same mask appear in this group shot of Flash props and weapons (bottom left and right).
These new pictures above are from the prop’s latest owner where the original auction tags (from Sotheby’s) are present and still attached. Thankfully it seems the piece has been kept in pristine condition as private collection or no, it remains an important relic of the film’s history…