The latest wave of gen 4 pokémon are some of the hardest to catch in Pokémon GO, but not if you know how to get hold of a Sinnoh Stone.
Pokémon GO is constantly adding new creatures but the latest set are unusual, because theyre all evolutions of ones that are already in the game.
The likes of Rhyperior, Magmortar, Electivire, Mismagus, Gliscor, PorygonZ, Honchkrow, Weavile, Roserade, Togekiss, and Dusknoir cannot be caught in the wild like regular pokémon and wont evolve using just candies.
What you need instead is a special item called a Sinnoh Stone, which works similar to items like sun stones and other evolution items.
How do I get a Sinnoh Stone?
The only way to get one of the special items is to complete a seven-day field research breakthrough. That means you have to complete one field research task a day for seven days, although it doesnt matter if you have a break in between days.
Once you complete the seventh task youll get all your normal rewards (which this month is a Shedinja) and the Sinnoh Stone.
Obviously thats going to take a long time if you want to evolve all the pokémon so make sure you prioritise which ones youre after or youll be well into next year before you get the one you really want.
Alternative ways of getting a Sinnoh Stone have been promised at some point in the future, but when that will be is currently a mystery.