Let’s just take a second to admire how bad-ass Steelix is. Seriously. Steelix is the second (and final) stage evolution of Onix, and is evolved by trading an Onix that’s holding a Metal Coat. Personally, I think Steelix will require 100 candies to evolve, but it could be 50 (or even 200, who knows!)
This is where things might start to get confusing for players who aren’t familiar with Gen 2. Hitmontop is the second (and final) stage evolution of a Pokémon named Tyrogue, and while Tyrogue isn’t actually a Gen 1 Pokémon, Hitmontop is on this list because Tyrogue’s other two evolutions are Gen 1 Pokémon: Hitmonlee and Hitmonchan.
I believe that when Tyrogue (and Hitmontop) are added to the game, Hitmonlee and Hitmonchan candies will turn into “Tyrogue” candies, and will be used to evolve Tyrogue into Hitmontop.
Therefore, hoarding Hitmonchan and Hitmonlee candies now might allow you to evolve a Tyrogue into a Hitmontop as soon as you encounter one after Gen 2 is released. Does that make sense? Good!
Blissey is the second (and final) stage evolution of Chansey, and let me tell you, she is one hell of a tank. Seriously, this girl can take a beating. The route to obtaining a Blissey in the original games was to increase your Chansey’s happiness to a certain point, level it up, and it would evolve. In Pokémon GO, however, I’d be guessing that it will just take 100 or so candies.
Kingdra is the third (and final) stage evolution of the Horsea/Seadra family, and in the original games, is only obtainable by trading a Seadra holding a Dragon Scale. Since it’s a third (and final) stage evolution, it will probably require 100 candies to evolve.