You need to talk to Professor Oak and he will ask you to show him Charmander/Bulbasuar/Squirtle, which is caught after talking to him either by you or buy it from someone else, doesn't matter, it needs to be Timid, Ada, Jolly or Modest for Charmander with 91 or more IVs , show the untrained char to Oak he will now ask you to train it to level 100 and make it Charizard, use the same Charizard you showed as charmander and he will battle you, if you win you will receive a Charizard Y stone.
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