In the Pokemon LeafGreen video game, Mew is not obtainable through an egg. Mew is a Legendary Pokemon which has only ever been available to players through Nintendo-sponsored special events, and is unbreedable. It is possible to receive glitched eggs called "Bad Eggs" which may corrupt LeafGreen's data, but this is rare.
No.
You can't get mew in firered or leafgreen.
mew and mew two
mew and mew two
There is no Mew 3.
Mewtwo? Plus you cannot get Mew in Leafgreen or Firered.
You can't catch mew on leafgreen you need gameshark codes for that
Mew two
Mewtwo, yes, if you have a FireRed or LeafGreen with Mewtwo.
Mew has to be traded from emerald and ho-oh you have to get from Pokemon colosseum.
Cheatcodes or luck.
Mew was distributed at an event once, but that is long over and sadly if you want a mew in leafgreen now, you'll need help from other games or you could use cheat codes.