A manga recently released in Japan that talks about the life of Satoshi Tajiri, the creator of the Pokémon franchise. A page from that manga was shown by James Turner (one of the designers who works for Game Freak on the Pokémon series) on his Twitter page that shows what appears to be scrapped designs from Pokémon that were intended to appear in Pokémon Red & Green.
The manga is part of a larger series that details the lives of various celebrities and important figures in Japan. The Satoshi Tajiri issue details his childhood love for collecting insects, which was one of the main inspirations for the Pokémon series. The manga also details the founding of Game Freak and the creation of Pokémon Red & Green.
One of the pages in the manga shows an internal Game Freak document with character designs for various Pokémon. This document appears to be part of an internal poll amongst the employees at the company to determine which ones they liked the most.
The document shows designs for four Pokémon that never made it into Pokémon Red & Green. These designs have also never appeared in later Pokémon games, though similar creatures that are based on the same animals & plants have shown up in the later generations.
Thousand-Yard Stare Crocodile
This is a design for what appears to be a Pokémon based on an alligator or crocodile. It would have most likely been a Water-type Pokémon at the very least. It may have been scrapped due to its creepy eyes or the fact that there were already a ton of Water-type Pokémon in the first generation of games.
We would later see Pokémon based on alligators and crocodiles in later generations, in the form of the Totodile and the Sandile lines.
This Pokémon appears to be a robotic reindeer or stag. It has the most machine-like appearance of any first generation Pokémon (save for maybe Magnemite and Magneton) which may be why it was scrapped, as they might have wanted to stay away from Pokémon that looked like robots. This Pokémon may have had a shot if the Steel-type existed in Pokémon Red & Blue.
We would see Pokémon based on reindeer and stags in the later generations of Pokémon games, in the form of Stantler and Sawsbuck, as well as with the Legendary Pokémon Xerneas.
The Covered Cactus
This Pokémon is partially covered by a note on the page, but it appears to be based on a cactus. The Pokémon appears to have a segmented body and would most likely have been a Grass-type Pokémon, with a possible Poison-type thrown on for good measure.
We would later see a cactus Pokémon in the form of Cacturne.
This Pokémon appears to be based on either a sawshark or a swordfish. The former is the most likely option, considering the sharp teeth and general shape of the body. It's also possible that this Pokémon might have been a combination of the two. This Pokémon would almost certainly have been a Water-type creature.
We would later see shark Pokémon in the form of Sharpedo.
The Lost Pokémon?
We have known for a long time that a lot of Pokémon had to be scrapped during the development of Pokémon Red & Green, due to the memory limitations of the Game Boy cartridges. The creators only had enough room to fit Mew on the cartridge after the debugging tools were removed, which shows you how little space they had to work with.
The blank spaces that were left behind in the date of Pokémon Red & Blue were an important part of the MissingNo glitch, which means that these unused designs may have been removed from the game and their spot was taken by the garbled glitch Pokémon and its ilk. It is due to the absence of the Pokémon seen above that we were given any nightmarish glitch Pokémon at all.
It's telling that these Pokémon designs were never used in later games in the series, which suggests that they were unpopular with the Game Freak staff. This doesn't mean that these designs will go unused forever, especially with the rumors of the Pokémon games on the Nintendo Switch returning to the Kanto region. We may still have a chance to use the cyborg reindeer and the blob cactus Pokémon in the future Pokémon games!