Complete the Pokédex

Completing the Pokédex is one of the most important goals in the Pokémon games and is used to unlock many of the necessary things to get PokéGods.

Origin
As one of the most important goals empasized during the games, it seemed odd to many that only the Diploma could be obtained after beating the game. This led to speculation of how it could relate to PokéGods and became a staple in many codes. Sometimes, variations were created, with 151 Pokémon (including Mew), 152 Pokémon (including Mew and Pikablu) or an obscure number higher than 150.

Mew
See also: Mew 

After catching all 150 Pokémon, it was thought that Mew could be obtained. This was proven wrong fast, causing people to speculate how else you could get Mew. Some said you had to go to the Hall of Fame or added more requirements.

Mr. Psychic
See also: Mr. Psychic 

Mr. Psychic was often used as an activation code to getting the PokéGods with certain requirements. One of these was often catching all 150 Pokémon.