You can Continue training or visit the Sevii islands
The Cerulean Cave
sadly,no
You can't get mew in firered or leafgreen.
Its not possible to get mew in firered only emerald can via Nintendo event.
You can't catch it on Firered you can only catch it in Emerald
no because there isn't a mew-three just mew and mew-two sorry
No
Cerulean cave
Pokemon firered emerald
Nope, you have to trade him.
can't but you can get one from emerald if you have the old sea chart and catch mew at faraway island.
The only legit way to obtain Mew is through a Nintendo event. In FireRed and LeafGreen you will need an event-only item to travel to the last two islands where you can catch that pokémon.