To complete the national pokedex, you must obtain all the the Pokemon that have been released. Here are some ways to get them.
- Just search in the tall grass and in caves.
- You will need to trade with Black to get some Pokemon because they don't appear in White.
- Check the electric boards in the gates and they will tell you where you can find outbreaks of rare Pokemon.
- Use poketransfer in the lab on route 15. This is helps get you Pokemon from other reasons and can really help.
- Make sure you attend all the wi-fi events to get Pokemon such as Genesect.
This is a hard trial, but it is worth it in the end because you get a shiny charm!