Somewhere, out there, exists an early prototype of the first Pokemon game, and thanks to a group of Pokemon fans, they might have allowed for the public to get a glimpse at some of the interesting bits and pieces within, similar to the Spaceworld Gold and Silver beta from last year. According to Helix Chamber, the site that managed to get ahold of these assets, an anonymous source contacted them, claiming that they had a prototype Generation 1 Pokemon game. After trying to contact this mysterious person, they were given a zip file that contained assorted files that were ripped right from the ROM. Though they refused to dump the ROM in full, (which is potentially concerning, in regards to the validity of the files) there's some never before seen early designs that would later be cut or repurposed for the final release of Pokemon Red and Green.
First revealed was an early working logo for Pocket Monsters, with an included unfinished Rhyhorn in the center. Also supplied were back sprites for these prototype Pokemon, but no front sprites were given, nor did the owner give a reason for omitting them. Front sprites were made in an attempt to re-create what could be, but they are in no way official, or part of the "leak", only existing as artistic interpretation.
Around the middle of last summer we were approached by someone who claimed to have Gen 1 prototypes and wanted to remain anonymous. We communicated via a private IRC channel of their making, and they provided us with some answers.— Helix Chamber (@helixchamber) February 18, 2019