You find a cave, go into it, then find a legendary pokemon, catch that pokemon, and then leave the cave.
No
Yes you can pick either of them.
There is know such thing as regifire.
no but you will find most pokeon at and around stark moutian.
You have to beat the eterna city gym leader.
You can't catch a charizard in pokemon pearl.
NO you cant catch syther in Pokemon pearl
No, you cannot catch Cyndaquil in Pokémon Pearl.
If you catch each 'letter' of Unown and keep them in the PC, they will merge into Unownus, a legenday pokémon that's one of the most powerful to this date.
neither of them is better, they are both the same, but in diamond, you catch dialga, and in pearl, you catch palkia, and you can catch different Pokemon in each game for example: you can catch this Pokemon in diamond, but not pearl but: you can catch this different Pokemon in pearl, but not diamond
you can certainly catch Dioxies in the game Pokemon pearl