There was a prototype of Bubsy in Claws Encounters of the Furred Kind, that was (according to the description of it) LESS polished than the original. Which is very interesting.
The price was 799$, but no one has ever bought that.
However, there is a picture of the cartridge and the tittle screen of it.
The theory of this one is that it might have some screenshots of the prototype of this game besides the title screen. It's proven by looking threw magazines, that is mentioned and look at screenshots of the game and see, if there's any difference. One was even found in this commercial. Here are screenshots I've found so far and the comparison.
There were two hot dogs in level 4, but there's only one hot dog in the final.
In level 7, there was a shark, but not in the final.
For this one, it doesn't exist in the final, because I can't find this place.
Ok, it's not much different from the final, but it's interesting non the less.
Did you know?
Interesting enough, there's another NTSC prototype of the same game (with a cartridge), that was found by Nullifidian on Ebay in 2007. It costed €199.95 (or $247.08).
There's also a PAL prototype of it.