Porygon does not evolve at a given level: you have to trade it while it is holding the Up-Grade to evolve into Porygon2. Then trade that while holding the Dubious Disk to get a PorygonZ.
the upgrade is used to evolve porygon into porygon-z
You will have to evolve a Porygon. By evolving it you have to trade it while it is holding an Up-Grade.
It is used to evolve Proygon2 into Porygon-z.
You use it on a porygon and it will evolve.(Pokemon Diamond, Platinum, and Pearl only.
Trade it while it is holding a Dubious Disc.
mightyena doesn't evolve on Pokemon pearl, he doesn't evolve in any Pokemon game!
In Pokemon Platinum (I don't know about Diamond and Pearl), Porygon is located in a house directly behind the Pokemon Center. If you want to evolve into Porygon 2, trade it holding a Up-Grade, and if you want to evolve Porygon 2 into Porygon Z, trade it holding a Dubious Disk. I do not know where htese items are found. If you want to get Porygon the harder way, use Pokecheck.
Buizel evolve at level 26.
evolve snowver at level 40
IT DOESN'T EVOLVE
You'll to make it hold an Upgrade and trade it. For Pokemon Pearl and Diamond at least, you'll need to make it hold an Dubious Disc as an bonus and trade it.
Porygon24, A Porygon2 with a Top hat but you require a Top Hat of Gonitude which can only be recived by completeing the Pokedex, defeating the champion 24 times, and the hardest part having maximum money. If you wimp out you can get a Dubious Disc which Porygon2 holds while trading to get a very lame Porygon-Z or AKA Porygon-Zero