its in the island after u beat the elite 4
There is no Battle Frontier in Pokemon Diamond and Pearl. Only the Battle Tower.
just keep winning the battle tower till you face him
battle tower 48 bp
Well, Its a thing you do after you complete the game. so i guess
you can evolve gligar into gliscor by giving gligar a razor fang and levelling it up at night, you can buy the razor fang at the battle tower or you can find it somewhere outside the battle tower.