try transferring Pokemon back and forth from diamond, pearl, or platinum. that way, the pokedex in both games are filled.
i believe your answer is the pokedex
Fill up the rest of your Pokedex!
You have see to many different pokemons. Then you will fill it (you have to every Pokemon to get national pokedex).
you need 200 Pokemon to fill the whole pokedex
You need to trade a Chikorita from Pokemon heartgold or soulsliver
you can't
To rebuild the Burnt Tower in Pokemon HeartGold and SoulSilver, you must fill up your pokedex. By the time that you finish your national pokedex, the Burnt Tower should be restored to its previous state. However, I am not sure what you can do in it when it is rebuilt.
youhave to beat the johto league
No, sorry.
just use the Pokemon global trading system. if you have platinum pearl or diamond it is in jubelife city. and if you have heartgold or soulsilver it will be in goldenrod city.
You can catch Lombre in Pokemon HeartGold in the Safari Zone at a waterside area once you receive the National Pokedex.
To research Pokemon, and fill up their Pokedex.