Deafeat elite four lots times LeafGreen?

Answer 1

nothing happens.

but people say if you beat the elite four many times, that a person drops a berry and it ends up being a ticket to birth island. but its not true.

if you beat the elite four 12 times mew will then be wild inside curulean cave, and after u catch mew celebi will be wild inside victory road.

EDIT:

You don't get anything from beating the elite four over 1 time except exp points for your Pokémon. And as for "Mew and Celebi coming out" that is completely false. You can't catch Celebi at all in Fire Red or Leaf Green and you can only catch Mew if you have the pass for 8 and 9 island (birth island and navel rock)

On birth island you can catch deoxys, when on navel rock you get catch Mew and the legendary pokémon Ho-Oh.

The only other way to catch these pokémon is to use something like GameShark which is a cheating device. I wouldn't use it my self because cheating takes the fun and point out of the game and also it can harm your vba. (visual boy advance).