You cannot "catch" the Pokemon that can never be caught. What you can do, is convince him to choose you as his companion. You do this by giving him gifts and being kind to him, or by providing help when he is in trouble. or you can trade from another game
He never caught one
No, Mewthree cannot be caught in Pokemon Pearl, because it never existed in the game. You would have to import Mewthree into the ROM to be able to catch it.
Catch Pokemon you already have caught
Giratina
You can't catch one.It can only be caught in Pokemon Pearl and Diamond
raikou cannot be caught on Pokemon ruby
You don't Zekrom is caught on Pokemon White.
Every time you see a Pokemon that you haven't caught (if it has a little pokeball symbol by its name then you caught it already) then catch it right away. Then once the game it beaten look on your pokedex for the ones that you haven't caught. POKEMON MASTER * INFINITY
It releases the Pokemon you have just caught =( sry
It should give you an option to after you catch it
It is possible to have caught all 649 eventually.
catch all the Pokemon, some Pokemon will need to be caught on Sapphire and traded.