Mew, the Mythical Pokémon, is catchable in the first generation game but only through glitches and cheats.
Due to a glitch, in the first generation of Pokémon, the move “Focus Energy” was essentially useless. Professor Oak was coded with an entire Pokémon well-balanced team at his disposal but was not included in the post-game, however there are glitches one can do in order to start a battle with him.
Around this time it is also when the Pokémon were individually named. The game had to be entirely reprogrammed since it could not simply translate the Japanese to English. The game was originally called “Capsule Monsters.” because they thought the characters were too cute for American children. The designers of the game wanted to change the characters before releasing in the U.S. They were released as Red and Green in Japan 2 years prior.
