You have to use sunny day in a battle, and then it will go back to normal after sunny day ends or you end the battle.
either way works
You train your Pokemon to lvl 100 or you can find some at the battle frontier in the place where you rent Pokemon and select open level in Pokemon platinum
First open up the calculator on ur poketch, type in the Pokemon you wants national dex number, then enter the level u want it.
if you get lots of badges, it will eventually open for you.
You have to get the key from the wind works and then you could open it.
you need a mystery gift
Press X on your keypad
it opens once you get the national pokedex
you need an action replay
lileycove? where is that I've never heard of it
There are level 50 and open level options
you have to get a members pass with an action replay