I'm pretty sure that's when you have to go to the mountains and battle dialga. Then get the eighth badge.
In Diamond, Badge 5 can be gotten by defeating Fantina in her Gym in Hearthome City.
the seventh gym badge snowpoint gym
when you get your seventh badge and you will head for mount cornet
any level up to 100
In Diamond, Pearl and Platinum 7th gym is in Snowpoint Town.
The 8th Badge in Pokemon Diamond is called The Beacon Badge.
Go to the team galatic base after battling the boss... P.S. I forgot the name
GET THE LAST BADGE......
With the seventh badge in Pokemon Ruby version, you can control caught or traded Pokemon up to level 70.
you go to the lake to battle team galatic and then you go to snowpoint city to get your seventh badge.
You go to get your 7th Badge in Mossdeep City.
You get the seventh gym badge after you defeat the snowpoint gym leader Candice she carrys the following Pokemon .... Snover, Sneasel, Medicham and Abomasnow and if your wondering how i know so much i am the Pokemon champion so you can send me questions anytime My name on wikianswers is ILovePokemon GOOD LUCK ON YOUR GYM BATTLE!!!!!!