You'll need it to have high Happiness/Friendship in order to evolve it.
Level 18.
Level 30.
Level 30.
level 28
Level 25
Level 37.
Level 26
at level 40 it should evolve into drapion
Spiritomb doesn't evolve.
you have to evolve it with a water stone
Donphan doesn't evolve.
There are not trainers with a Buneary in SoulSilver.