Machoke>Machamp
Haunter>Gengar
Electabuzz>holding electrizer>Electravire
Onix>holding metal coat>steelix
Clampearl>holding Deepsea Scale> Gorebyss
>holding Deepsea Tooth> Huntail
Feebas>holding Beauty Scale>Milotic
Magmar>holding magmariser>Magmortar
Seadra>holding dragon scale>Kingdra
Sycther>holding metal coat>Scizor
Slowpoke>holding Kings Rock>Slowking
Graveler>Golem
Kadabra>Alakazam
Poliwhirl>holding Kings Rock>Politoed
Porygon>holding upgrade>Porygon2>holding dubious disc>Porygon-Z
Dusclops>holding Reaper Cloth>Dusknoir
Rhydon>holding Protector>Rhyperior
machamp and haunter are the only ones
It only evolves through trade.
It will only evolve if you trade it.
Machoke evolves into Machamp only through trade my friend.
It varies from Pokemon to Pokemon levels they evolve on range from: 6-55. Some Pokemon only evolve under certain conditions: Some evolve if exposed to evolutionary stones like a fire stone, Some evolve only if you trade them to a friend, Some Pokemon evolve during trade but only if they hold a certain item like metal coat, Some Pokemon evolve if they have max friendship with there trainer, Some Pokemon evolve during certain times or evolve at certain areas, Some Pokemon will only evolve if there a specific gender.
Haunter only evolves into Gengar through trade. If you're using a generation 4 Pokemon game you can deposit Haunter into the GTS and trade for any other Pokemon in the GTS, then take back your Haunter and it will evolve.
Only by trade.
Graveler only evolves when you trade it with someone else. It evolves into Golem. This makes Graveler one of the Pokemon that can evolve at any level.
This is one of the pokemon that never evolves, unless you trade it to a friend. The only way of getting it to evolve into a machamp is therefore to trade it with someone.
Graveller evolves into golem only through trade. It doesnt need to hold any item.
In indigo, you don't need hold items to evolve them through trade. Just trade a Rhydon. Your welcome :P
Haunter will only evolve through trade.