It DOES NOT evolve by level.
When it's friendship with it's trainer is high, it'll evolve after leveling up once.
prinplup will evolve at level 36 in Pokemon pearl
mightyena doesn't evolve on Pokemon pearl, he doesn't evolve in any Pokemon game!
evolve snowver at level 40
Buizel evolve at level 26.
At level 48 he should evolve.
they evolve at level 20
IT DOESN'T EVOLVE
level 18
at level 30
level 50