Here's a list of pokemon that evolve when traded holding an item in Pokemon X and Y.
- Deep Sea Scale – Causes Clamperl to evolve into Gorebyss when traded. Held item by Chinchou, Lanturn, Gorebyss, Relicanth. Also one can be found Western island of Azure Bay.
- Deep Sea Tooth – Causes Clamperl to evolve into Huntail when traded. Huntail can be found on Route 12 (Super Rod, X only). Held item by Carvanha, Sharpedo, Huntail, Basculin. Also one can be found Western island of Azure Bay.
- Dragon Scale – Causes Seadra to evolve into Kingdra when traded. Held item by Horsea, Seadra, Dratini, Dragonair. Also one can be found in Terminus Cave.
- Dubious Disc – Causes Porygon2 to evolve into Porygon-Z when traded. Purchase from Battle Maison, 32BP.
- Electirizer – Causes Electabuzz to evolve into Electivire when traded. Purchase from Battle Maison, 32BP.
- King's Rock – Causes Poliwhirl to evolve into Politoed when traded. Politoed can be caught on Route 19 (Super Rod).
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And causes Slowpoke to evolve into Slowking when traded. Held item by Poliwhirl, Poliwrath, Politoed, Hariyama, Hawlucha. You receive one from Lysandre at Lysandre Cafe - Lumiose City after getting your Voltage Badge.
- Magmarizer – Causes Magmar to evolve into Magmortar when traded. Purchase from Battle Maison, 32BP.
- Metal Coat – Causes Onix to evolve into Steelix when traded. And causes Scyther to evolve into Scizor when traded. Held item by Magnemite, Magneton, Metang, Bronzong. Also one can be found in Poke Ball Factory hidden next to a conveyor belt.
- Prism Scale – Causes Feebas to evolve into Milotic when traded. //note these Pokémon are currently unavailable in X/Y. One can be found in Couriway Town.
- Protector – Causes Rhydon to evolve into Rhyperior when traded. Purchase from Battle Maison, 32BP. Also one can be found in Lost Hotel.
- Reaper Cloth – Causes Dusclops to evolve into Dusknoir when traded. Purchase from Battle Maison, 32BP. Also one can be found in Terminus Cave.
- Sachet – Causes Spritzee to evolve into Aromatisse when traded. Purchase from Battle Maison, 32BP. Also one can be found Cyllage City, Route 12.
- Up-Grade – Causes Porygon to evolve into Porygon2 when traded. Purchase from Battle Maison, 32BP.
- Whipped Dream - Causes Swirlix to evolve into Slurpuff when traded. Purchase from Battle Maison, 32BP. Also one can be found Skiddo Farm, Route 12.
- Up-Grade – Causes Porygon to evolve into Porygon2 when traded. Purchase from Battle Maison, 32BP.
- Whipped Dream - Causes Swirlix to evolve into Slurpuff when traded. Purchase from Battle Maison, 32BP. Also one can be found Skiddo Farm, Route 12.