Lots of training :) just redo the elite 4 over and over again it can get monotonous though.
Charizard doesn't evolve.
There is not a charizard in any game other than Red, Blue, Green, Yellow, FireRed, or LeafGreen. In those games, Charmander is available as a starter, and you have to train it up to Level 100.
Yes, you train them my charizard got level 100 last night
Get a team of level 100's like me. I have level 100 Charizard, Mewtwo, Rayquaza, Latias, and Kyogre. I also have a level 97 Sceptile and a level 91 Blaziken.
Charizard learns Heat Wave at start in Pokemon FireRed. In Generation IV, Charizard learns it at level 59. In Platinum, HeartGold and SoulSilver, Charizard can also learn Heat Wave by move tutor.
only by training, charmeleon evolves into a charizard at level 36
Charmander (16) = charmeleon (36)= Charizard
The last move, in fire red, that Charizard learns is Fire Spin. That is at Level 55.
100
you go to the game corner in celadon and buy it or level up a charizard
You use a level 100 charizard.
There really isn't a strongest. For that all depends on the stats, level, and of course moves. Charizard is a good fire pokemon, but so is Arcanine!