There are many different ways to fill the national Pokedex. You can play FireRed, Leaf Green, Sapphire, Ruby and Emerald and transfer the Pokemon via Pal Park. Use the global link to trade for the missing Pokemon or trade with friends.
try and fill the national dex
yes you have to migrate
fill up sinnoh Dex and go to the Professor and Oak will come and upgrade your Dex
You try to fill up your pokedex so you can get the national dex. When your done with that then you try to fill the natonal dex by migrating Pokemon to pal park. There are alot of legendaries that you can only get after you get the national dex
well you need to fill all your sinnoh dex then talk to rowin and this guy (Oak) he will upgrade your dex then you have the national dex.... hope that helps, Tina :D
get a action replay
Capture all pokemons.
You complete your sinnoh pokedex, then go to your hometown and get the national 'dex then go to pal park and migrate pokémon from ruby, sapphire, leafgreen or firered.
You just get on with the game but go to the professor incase
After you fill your whole dex and beat the E4.
you should find every Pokemon in sinnoh. i going to find all the pokemons in the national dex ;)
If you want to fill your Sinnoh Dex, look on websites. There are lists of where to see every Sinnoh Pokemon. If you want to fill your National Dex, you have to import them from your GBA games.