The Prototype Gen 1

Notes:

A group of Pokémon fans recently found a prototype build of Pokémon Green, in it were some original Pokémon that were left out of the final release.
A pre evolution Zubat, a third evolution for Cubone resembling Kangaskhan, third row from the bottom next to Haunter, no front sprites exists, and the planned third Pikachu evolution Gorochu, to the left of Charmander near the bottom right.