How can you migrate Pokemon?

Answer 1

First you need to finish Diamond or Pearl. This means you need to defeat the entire Elite Four, and get into the hall of fame. After doing so, Prof. Oak will let you know that Pal Park has opened.

Now I suggest you turn on your GBA game (after saving your game on Diamond or Pearl first) and select SIX Pokemon you wish to migrate ahead of time. YOU CANNOT MIGRATE POKEMON THAT ARE IN YOUR PARTY. You cannot choose less than 6 Pokemon to Migrate (weird O.o)

After pre-choosing your Pokemon (Keep your GBA cartridge in your DS), go to the start-up menu of your game then you will see an option called "Migrate from XXXX". XXXX being whatever GBA game you have inserted into your DS. Next select your Six Pokemon and your game will prompt you about migrating them.

DO NOT TURN OFF YOUR DS!!! Here is why:

Your Pokemon that you have migrated are at Pal Park. This means that if you don't re-catch your Pokemon (100% catch rate by the way) they're gone forever. So plan to catch them right away when you migrate your Pokemon so you don't forget!

After you make enough preparations, go into the pal park and start searching for your Pokemon, there are 5 areas of capture:

Field

Woods

Cave/Mountain

Shallow Water

Sea

Remember what Pokemon you migrated, because you're going to find your Pokemon in the areas that match your Pokemon the most. Most Legendaries will pop up in the Cave/Mountain area. You have unlimited time to capture your Pokemon, but the faster you do so, the better your personal score and you get a prize. Just remember to capture them all or they will be gone forever.