You can't, but you can by breeding Pokemon or trading. However in Emerald you can by duplication
trade
There are two possible ways: Choose Treeko as a starter Pokemon Or By trading
Trading or action replay. sorry if that was no help. :[
no you can catch a charizard in pokemon ruby you can get it as a kanto starter
mudkip
Torchic, Mudkip, and Treecko.
Mudkip is available as a starter pokemon in more than one games. They are Pokemon Ruby, Pokemon Sapphire, Pokemon Emerald, Pokemon Omega Ruby and Pokemon Alpha Sapphire.
trade
you can't.
Pokemon Emerald,Ruby and Sapphire
wait you mean ruby is sinnnooohhh
Ruby, Sapphire and Emerald.