beat the #?*@! gym leader
The 8th Badge in Pokemon Diamond is called The Beacon Badge.
beat the league
Wher there used to be a power failure
By beating the gym leader
I'm pretty sure that's when you have to go to the mountains and battle dialga. Then get the eighth badge.
The 8th gym is in Sunyshore, but you will be unable to go there until after you beat Cyrus on Mt. Coronet.
earn it.
the ground gym
Beat the gym leader
== == You get the 8th gym badge in Sunyshore City. Hope this helps
== == == ==
you must beat the eighth gym leader and he will give you the badge.