By "Crystal" I suppose you're meaning a Shiny Pokémon.
Shiny Pokémon are extremely rare. Every time you encounter a wild Pokémon, you have a slim chance of finding a shiny one. It is around 0.01% chance of finding one.
There is no 'platnium', but you can find it on wild pokemon.
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You can't find Registeel in Pokemon Platnium. You just migrate it in Pokemon Ruby, Pokemon Sapphire, and Pokemon Emerald.
Honey Trees
in the trophey garden
in girantinas cave
No, you'll have to trade it from Platnium. Which in Platnium you find it in the Rock Peak Ruins.
you cant that's a Pokemon move and Pokemon can learn it
use your map to find out
you have to trade him from Pokemon platnium
U have 2 trade him
you can find one with a traner on 216