you need to beat the elite four and have the national dex
same as diamond/pearl
After getting all eight badges sail upwards from sunnyshore city until you get to victory road. Get through victory road and you will be at the Pokemon league.
Look near the end of victory road and you might find it
When you surf in the basement of Victory Road, there should be some Lapras hanging about.
Use waterfall above Sunyshore and it will take you to Victory road. Go through Victory Road's maze and you'll find yourself at the elite four.
.....The Pokemon league......
victory road
VICTORY ROAD IS BEST
Make your way through route 223. When you get to a Pokemon Centre, walk into the cave on the left and you will be in victory road.
victory road is north of sunyshore city a the end of the cave before Pokemon league
in twin leaf town
same as diamond/pearl
After getting all eight badges sail upwards from sunnyshore city until you get to victory road. Get through victory road and you will be at the Pokemon league.
Beat the 8th gym leader and have a Pokemon that knows Surf and Waterfall to get to Victory road. go though victory road battle your rival and there you go.
all you have to do is follow the diamond/pearl walkthrough for victory road. I suggest looking up pokedream.com
In platinum,pearl, and diamomd on the way to the victory road
Go past victory road you dummy