Pokémon Red and Blue went through a lot of changes during development, which included Pokémon having different names from the final version of the game. The alternate names for some of the original Pokémon have been revealed online and some of them are way better than the ones that were chosen.
The original Pokémon games were designed with the Japanese audience in mind, as the localization process didn't begin until after Pokémon Red and Green were released. It wasn't as common for Japanese RPGs to be localized in the West in the late '90s, especially for franchises aimed at children. As such, Pokémon Red and Blue underwent a lot of censorship and localization changes, in order to make them palatable to European and North American audiences.
According to Bulbapedia, early promotional material for Pokémon Red and Blue made the rounds before the games were released. These included different names for familiar Pokémon, some of which were terrible, like calling Omanyte Ess and Omastar Kargo. However, some of the original names were awesome and it's a shame they weren't chosen for the final version of the games.
Pokémon Beta Names That Should Have Been Used - Rattatak
Rattata is one of the original junk Pokémon, even taking the notorious F.E.A.R. strategy into account. The feeble rodent almost had a much more intimidating name, as it was referred to as Rattatak in the promotional materials for Pokémon Red and Blue. It's unclear why this name was changed, considering the word attack is used throughout the Pokémon games.
Pokémon Beta Names That Should Have Been Used - Foxfire
Foxfire is a type of glowing mushroom that commonly grows on deadwood. It's also the perfect name for Vulpix, which is a Fire-type fox from Pokémon Red and Blue. The decision was made to go with a name that uses Roman numerals instead, in order to tie into the tail numbering theme. If the three-tailed Vulpix pre-evolution from the leaked Pokémon betas was canon, then this naming convention might have made more sense.
Pokémon Beta Names That Should Have Been Used - Parasyte
Paras and Parasect have one of the most disturbing inspirations in the entire Pokémon series. They're inspired by cordyceps fungus, which attaches itself to the bodies of insects and takes control of their bodies. The monsters in The Last of Us series are meant to be the result of cordyceps that gain control over human hosts. The original name of Paras was Parasyte, which is a far cooler name and is more indicative of its inspiration. It's possible that the name might have been considered too much for a kids' game, though that hasn't been confirmed.
Pokémon Beta Names That Should Have Been Used - Skullkraken
Gyarados is one of the few Pokémon that has the same name in English and Japanese. This means that the name is meaningless in English, as the Japanese name can be broken down into references to different words for violence. In the promotional materials for Pokémon Red and Blue, it was called SkullKraken, combining its violent nature with the famous sea monster. Much like how Zubat has a better name in France, Gyarados also has a better international name, as it was called Léviator in the French version of Pokémon Red and Blue, which is a take on the word Leviathan.
Source: Bulbapedia