the ones i know of is
porygon to porygon 2 to porygon z
gravaller to golem
Haunter to gengar
Onix to steelix
It must be traded to evolve.
No, you must trade the certain Pokemon that need to be traded to evolve to make them evolve.
Haunter does not evolve into Gengar at a certain level. Haunter needs to be traded to another player. Once he is traded, he will evolve.
Porygon can evolve at any level since it needs to be traded in order to evolve however it needs to be holding an Upgrade while it's being traded in order to evolve.
Graveler must be traded for it to evolve into Golem
Graveler evolves into a golem. he will only evolve if he is traded.
It does not evolve by levelling, it evolves when traded for a Shelmet.
It will only evolve it if is traded.
Gravler has to be traded to evolve.
Gurdurr doesn't evolve by a stone, it will only evolve when traded.
a Pokemon that has to be traded to evolve can be any lvl you want it to be you get it the Pokemon the same lvl that your Pokemon was it does not grow a lvl when it is traded
It will evolve when it is traded while holding a dragon scale.