Check out the pitch documents for the original Pokemon games

Preservation website Helix Chamber has re-scanned and restored some pages from the original Pokemon pitch presented by series co-creators Satoshi Tajiri and Ken Sugimori back in 1990. 

The documents offer some interesting insights into the formative days of the now globally recognized franchise (originally called 'Capsule Monsters'), including concept art, sprite designs, and map layouts -- including some ideas that were scrapped, and others that eventually made it into the final product. 

For instance, the booklet features a piece of art that fans will clock as the inspiration for the iconic Gengar vs. Nidorino battle that plays out during the opening credits of Pokemon Red and Blue (or Green in Japan). 

It also contains the early sprite designs for a number of pocket monsters including Rhydon, Kangaskhan, Voltorb, and Slowbro, all of which are instantly recognizable, and didn't seem to change much during development. 

A conceptual map of Kanto also reveals that the original games might've featured a wider variety of landscapes, such as a desert area, along with the ability to trade items as well as Pokemon. 

Incidentally, item trading was added in Pokemon Gold and Silver, where players were given the ability to attach items to Pokemon before trading. 

As you can imagine, there are more tidbits where those came from, so be sure to check out the full set of design documents over on Helix Chamber.