Manafi
To get Manfi you must download it from Pokemon Ranger.
National Dex/Completing the Shinou Dex
Luckily, in this game, all you have to do to complete the Shinou Dex is SEE all the Pokemon in the Dex, as opposed to catching them like in previous games. And once you see all the Pokemon, you unlock the National Dex. There are 151 Pokemon in the Shinou Dex, but not all the new Pokemon are included in it.
Hatch Eggs Faster
To hatch eggs faster, put it next to a pokemon with magma armor. NEXT TO IT!!! And then it reduces the steps needed to hatch.
Getting all Pokemon
You cannot catch all Pokemon in this game. You must trade them from your Game Boy Advance Pokemon games. In this game, you can get all the fourth generation Pokemon, but only about fifty original Hoenn/Kanto/Johto Pokemon.
Unlock Pal Park
Pal Park will be on route 221 when you get the National Dex.
Elekid and Magby
When you have Pokemon FireRed/LeafGreen version in your GBA slot, it will unlock two Pokemon that cannot be found elsewhere.