There are a lot, so i cant tell you them all, but i will tell you there is a lot.
you cant catch him in there only in trade
If you get squitle as your starter, once you get the national dex, it will be a roaming Pokemon
Its not possible to get mew in firered only emerald can via Nintendo event.
you have to mirate growlif from Pokemon firered. To get growlif in firered you need the national dex then you can catch it on route 2.
After you fill your whole dex and beat the E4.
catch all of the Pokemon in the kanto region then go and see pro. oak and he will give you the National Dex
you must have the national pokedex at search for it in the trall grass and catch it or trade it from firered or leafgreen
To get Pokemon firered on PC download a vba and Pokemon firered ROM
You can catch a Ho-Oh at Navel Rock in Pokemon FireRed.
You can catch Moltres at Mt. Ember Peak in FireRed.
you can not catch him
you can't unless you get the national pokedex and trade for one in sapphire or ruby.