Level it up with max happiness. You can give it a soothe bell, and train it.
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It doesn't evolve at level you have to max its friendliness and it evolves into Crobat.
Golbat only evolves when it's loyal to it's trainer which only occurs after training it for awhile, giving it items and other good things.
Dunsparce does not evolve.
Your Golbat needs to be happy with you. If you din't have one you can catch them in the Ice Path (or any other cave that you know has a Golbat)
You can't evolve magneton in soul silver. You can only evolve it by trading it back to Diamond or Pearl and training it at Mt. Coronet.