Here are some real proto-prototypes!
These figures are described as being made of "white wax". Making an object out of wax is actually a (likely WAS, at this point) common prototypeing technique. Wax is carve-able easily and holds detail well. It is also likely inexpensive to work with, and molds can easily be made from it. It is rare to see such items, because companies usually keep these to themselves, or they're somehow destroyed in a process. It is also likely that any waxes are 'the only one' because of its prototype nature.

These are LIKELY early Tomy mini figures.
It is probably the prototype for their early Sonic 2 era PVCs. Notice how they're not really that accurate, even after Sonic 2 showed the back of the characters. Tails has a full fringe on the back of his head, about no legs at all, is super fat/big body, and is not particularly cute. (The Tails sprite in Sonic 2 was always quite cute) Sonic also has very small...eye...really large single finger & bigbody. Because the final actually produced PVC or display figure may be different from these sculpts, it's hard to tell what these are prototypes of. Can you take a guess? Write in if a figure looks familiar.
Notice that they're not holding up too well, there's cracking and fracturing on the figures. Tails' hand, Sonic's shoe/ankle both have crack/chips, revealing this is no ordinary plastic material. A rare look at true prototypes!