Easy, you can't, but you could migrate it from the older games.
Honey Trees
you cant that's a Pokemon move and Pokemon can learn it
you have to trade him from Pokemon platnium
U have 2 trade him
you have to find the man that deletes any move
There is no 'platnium', but you can find it on wild pokemon.
You can't find Registeel in Pokemon Platnium. You just migrate it in Pokemon Ruby, Pokemon Sapphire, and Pokemon Emerald.
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You can find Mewtwo in the Cerulean Cave.
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
Mewtwo is found in cerulean cave.
It's impossible to find Mewtwo in Platinum.
Mewtwo is at level 70 when you find it on leaf green.