An early version of Pokémon Gold and Silver, featuring dozens of Pokémon cut from the final release, has been found by fans and posted online.
The build comes from Nintendo's Space World promotional event all the way back in November 1997. Fans over at the The Cutting Room Floor have been poring over the discovery, and have found numerous unused designs still lingering in its code.
The leak has astonished many Pokémon fans. The build includes alternate, unfinished versions of familiar locations and work-in-progress Pokémon designs kept under wraps for more than two decades by the famously secretive Pokémon Company.
Notably, Pokémon's second generation of games would have boasted many more baby Pokémon, including unevolved forms of Generation 1 creatures such as Meowth, Vulpix, Ponyta, Tangela, Goldeen, Grimer, Growlithe, Paras and Doduo.
Early versions of Tangela and Likitung evolutions Tangrowth and Lickilicky, and Mr. Mime baby Mime Jr. - all of which eventually turned up in Generation 4 - can be seen. Pinsir would have also gained an evolution, which looks similar to the Mega Evolution it finally gained in Gen 6.
Evolutions for Ditto, Weepinbell, Farfetch'd, and Qwilfish are also in the code. These never made it into later games at all.
Two of the game's starter Pokémon were also different. Instead of Cyndaquil, players would have had the choice of a fire-type bear which evolved from a cub to lion-like creature over its two evolutions.
The game's original Water-type starter, meanwhile, looks like it was re-used years later for Pokémon Sun and Moon's Popplio. It would later be replaced by Totodile.
Other, all-new Gen 2 species were canned completely. There was a bell-wearing cat Pokémon which would have evolved into a larger, fiercer form. It looks a little like Generation 3's Skitty/Delcatty.
The shellfish-like creature now seen hanging onto Slowking's shell was designed to be its own separate Pokémon.
There would have been a tiger/mouse Pokémon which looks look a little like Gen 6's Dedenne.
Finally, a pair of panda-like Pokémon were planned. The latter looks a little like Gen 6's Pancham.
You can view a fan-made spreadsheet - or see them all in one big image below. Note the earlier versions of existing Pokémon which did see the light of day. One detail I was surprised by is that Dark-type Eevee evolution Umbreon was originally designed to be Poison type, and evolved via a Poison Stone item.
Will any of these show up in Pokémon Let's Go: Pikachu and Eevee? It's unlikely, as it looks like this year's Nintendo Switch Pokémon games are set to focus only on the series' original 151 creatures.