Question

I saw on this question that Galactic Lucario (sorry if I spelled his username wrong.) said something about a shiny charm.

Answer 1

A Shining Charm ups the chance of a Shiny Pokemon appearing.

This Key Item increases the likelihood that you will encounter Shiny Pokémon. When you have the item in your bag, then the chances of encountering Shiny Pokémon in the wild is increased to 300% of normal, making it a 1 in 2,370.6 chance. If, however, you're using the Masuda Method to breed, it increased it from 1 in 1,365.3 down to 1 in 1024.

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Comments

But you can only get it after catching the whole national dex.

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Yeah, I know.

Answer 2

You get the Shiny Charm after you've caught all the Pokemon in the National Pokedex
(I think you don't need event Pokemon).

It increases your chance of finding a shiny Pokemon by 300% of normal, making it a 1 in 2,370.6 chance.
If, you're using the Masuda Method to breed, it makes it 1 in 1024 to get a shiny.
Source