>>44037419Karrablast and Shelmet's dex entries explain it.
>Karrablast: These mysterious Pokémon evolve when they receive electrical stimulation while they are in the same place as Shelmet.>Shelmet: When it and Karrablast are together, and both receive electrical stimulation, they both evolve.Presumably, this same electrical stimulation is what causes other trade evolutions to evolve as well. The trade machine simulates the electrical stimulation they need to evolve.
