What Happens After You Catch All 150 Pokemon?by Chelsea Anderson ; Updated September 22, 2017
After defeating the eight gym leaders and the Elite Four, many trainers take on the challenge of completing the Pokedex given to them by Professor Oak at the start of the game. In the original "Pokemon" games for the Gameboy and Gameboy Color, there are only 150 Pokemon. Players trade between "Pokemon Red" and "Pokemon Blue," each of which has version-specific Pokemon, to catch them all and become a Pokemon master.
"Pokemon Red" and "Pokemon Blue" each have several Pokemon unique to that version. Without trading, filling the Pokedex and capturing all 150 Pokemon is impossible. Ekans, Arbok, Oddish, Gloom, Vileplume, Mankey and Primeape are all exclusive to the Red version, as well as Growlithe, Arcanine, Scyther and Electabuzz. The Blue version exclusives include Sandshrew, Sandslash, Vulpix, Ninetales, Meowth and Persian, in addition to Bellsprout, Weepinbell, Victreebel, Magmar and Pinsir.
At the start of the game, the player must choose between Bulbasaur, Squirtle or Charmander as his starting Pokemon. The other starters are unobtainable except through trade with another game cartridge, and without getting them it is impossible to catch all 150 Pokemon. Kabuto and Omanyte are fossil Pokemon found later in the game, and the player must choose between one of the two. The other must be traded for.
After catching all 150 Pokemon, the player can revisit Professor Oak in Pallet Town. He will evaluate your Pokedex and tell you that it is complete, then congratulate you. He does not offer any special rewards.
After speaking with Professor Oak, the player can go to Celadon City to obtain a diploma. After catching all 150 Pokemon, the Game Designer on the third floor of Celadon Mansion will give you the diploma. The top says "Diploma" and shows the name the player gave his character. The rest of the diploma says "Congrats! This diploma certifies that you have completed your Pokedex." It is signed by Game Freak. In the lower-right corner of the diploma, there is a sprite of the player character holding a Pokeball in his hand. There are no other rewards or special recognitions offered for seeing and catching all 150 Pokemon.
The 151st Pokemon, Mew, was available from certain special events hosted by Nintendo. It can also be found by exploiting glitches in the game or with a cheating device. Catching Mew is not necessary for completing the Pokedex, though it does have a Pokedex entry and Professor Oak will note that you have caught 151 Pokemon when you speak with him. Several glitch Pokemon, such as Missingno, are also present in the game but do not count toward the player's Pokedex.