Trade Evolution has long been a part of the core Pokémon games, and now it's coming to Pokémon GO! The system will work a little differently in Pokémon GO: when you trade certain Pokémon, the Candy requirement for their Evolution will be removed. Plus, Throh, Sawk, Basculin, Maractus, and Sigilyph will start appearing only in certain parts of the world.
Some of the Pokémon that will benefit from trade Evolution include Kadabra, Machoke, Graveler, and Haunter—Pokémon that could evolve only via trading in Pokémon RPGs since the debut of Pokémon Red and Pokémon Blue. Don't worry if you've already traded for one of these Pokémon—these Pokémon will retroactively qualify for the trade Evolution benefit when they evolve. In addition, other Pokémon that evolve via trade in Pokémon RPGs—such as Boldore, Gurdurr, Karrablast, and Shelmet—are starting to appear in Pokémon GO, and they'll also be able to benefit from trade Evolution.
In addition to the Pokémon just mentioned, quite a few more Pokémon originally discovered in the Unova region will begin appearing in the world. Keep an eye out for Roggenrola, Tympole, Dwebble, Trubbish, Joltik, and more in the wild. Plus, you might find Timburr, Venipede, Tirtouga, Archen, Axew, and others when you hatch Eggs. Timburr will also begin to show up in one-star raids.
Depending on your location, a few more Pokémon will begin appearing in the wild, too. In North America, South America, and Africa, Throh will begin appearing in the wild (and in 10 km Eggs). Trainers in Europe, Asia, and Australia will encounter Sawk in the wild (and can find it in 10 km Eggs). Additionally, if you're in the southern United States, Mexico, Central America, the Caribbean, or South America, you may discover Maractus. And in Egypt or Greece, look for Sigilyph to start appearing. Lastly, Red-Striped Form Basculin will begin appearing in the eastern hemisphere, while Blue-Striped Form Basculin will begin appearing in the western hemisphere.
Start those trade Evolutions to get your hands on powerful Pokémon, and be on the lookout for more Pokémon originally discovered in the Unova region appearing near you.