So it looks like Generation IV Pokémon will be introduced into Pokémon GO soon. Generation IV has the distinction of having the most new evolutions of previously established Pokémon of any Generation, so keeping this in mind there are certain Pokémon you can catch right now that will help you to complete your Pokédex once Sinnoh Pokémon are introduced into the game. Below is a list of currently available Pokémon that you should start stocking up on, along with a description of what will likely be necessary for their eventual evolutions once Gen IV hits the game.
Roselia gains a new evolution in Gen IV in the form of Roserade, so catching a bunch of Roselia now will probably serve you well once Gen IV is introduced into the game. Roselia also gets a new baby evolution in Gen IV, Budew. Budew will likely only be available via Eggs, so there isn’t really anything you can do to prepare for that other than stocking up on Egg Incubators. However, since Roselia will go from having one evolutionary stage to three in Gen IV, it’s likely that Budew will evolve into Roselia with 25 Roselia Candies, and then Roselia into Roserade with 100 Roselia Candies. So you should probably try to catch quite a few Roselia so that once Sinnoh Pokémon come to the game, you’ll be able to evolve a Roselia immediately with the 100 Candies you’ve been collecting. It’s also worth noting that in the mainline games Roselia evolves into Roserade using a Shiny Stone, and while not all Pokémon that need Stones or other items to evolve in the mainline games need one to evolve in Pokémon GO, it’s possible that you’ll have to happen upon a Shiny Stone at a PokéStop before being able to evolve your Roselia. In fact, there are a lot of Pokémon in Gen IV that need items to evolve. When Gen II was introduced into Pokémon GO, only a few of the Pokémon that need items to evolve in the mainline games needed items to evolve in the mobile spin-off, so it’s certainly possible that Roselia won’t need a Shiny Stone to evolve in GO, but you should be prepared to visit a ton of PokéStops anyway to collect Razor Claws, Protectors, Magmarizers and whatever other evolution items may become necessary.
Aipom gains the evolution Ambipom in Gen IV, so you should probably collect as many Aipoms as you can to stock up on Aipom Candies. In the mainline games, Aipom evolves into Ambipom by leveling up while knowing the move Double Hit. Given how moves work in Pokémon GO, however, I can’t imagine they’d try to enforce this. Instead, they’ll probably just make Aipom evolve with 50 Aipom Candies.
Misdreavus and Murkrow
Both Misdreavus and Murkrow gain new evolutions in Gen IV and both need a Dusk Stone in order to evolve in the mainline games. Pokémon GO might include a Dusk Stone item that you’ll need to evolve Misdreavus into Mismagius and Murkrow into Honchkrow, which you’ll be able to get randomly at a PokéStop. Regardless of whether you do end up needing Dusk Stones or not, it’s likely that you’ll need 50 Candies for both of these Pokémon to get them to evolve.
In Gen IV, Sneasel evolves into Weavile when leveled up at night while holding a Razor Claw. This is a lot of rules to enforce, and since Sneasel is the only Pokémon to use the Razor Claw as an evolutionary item, I can see Pokémon GO forgoing all these complications and just requiring 50 Sneasel Candies for evolution. That being said, be prepared to visit a ton of PokéStops if a Razor Claw is necessary for evolution.
Magnemite and Magneton
The Magnemite line gets a new evolution in Gen IV, Magnezone. The Gen IV weird evolution methods continue with this one, as in the mainline series Magneton will only evolve into Magnezone by leveling it up in specific locations. Again, I don’t think this is very likely to happen in Pokémon GO and they’ll probably just require 100 Magnemite Candies to do the job.
Lickitung evolves into Lickilicky in Gen IV, and like with Aipom and Ambipom, requires a specific move to be known while leveling up to evolve in the mainline games. In Pokémon GO, you’ll probably just need 50 Lickitung Candies.
Rhyhorn and Rhydon
The Rhyhorn line also gets a new evolution in Gen IV, as Rhydon evolves into Rhyperior in the mainline games by trading a Rhydon that is holding a Protector. Again, you might need to get a Protector from a random PokéStop drop, but regardless of whether a Protector is necessary or not, you’ll probably need 100 Rhyhorn Candies to evolve Rhydon into Rhyperior in Pokémon GO.
Tangela and Yanma
Tangela evolves into Tangrowth and Yanma evolves into Yanmega in Gen IV. Both evolve by leveling up while knowing Ancientpower in the mainline games, but, once again, Pokémon GO will probably just necessitate 50 Candies for their evolutions.
Electabuzz and Magmar
Electabuzz and Magmar are more weird item evolutions in Gen IV, with the former needing to hold an Electirizer while being traded to evolve into Electivire and the latter needing to hold a Magmarizer while being traded to evolve into Magmortar. Electirizers and Magmarizers will likely be available from PokéStops if necessary for evolutions, but either way, both new evolutions will probably require 100 Candies.
Togepi and Togetic
Togetic evolves into Togekiss through use of a Shiny Stone in Gen IV, so once again, you may need to acquire a Shiny Stone from a PokéStop, but you will almost definitely need 100 Candies for the evolution as well.
Eevee gains both the Grass-Type Leafeon and the Ice-Type Glaceon as evolutions in Gen IV, and we can probably expect that both will be attainable by having Eevee randomly evolve into one after giving it 25 Eevee Candies or by giving it a specific nickname before evolving it, as is the case with the other Eeveelutions. Of course, we’ll have to wait for dataminers to find out what those nicknames are once Gen IV is introduced into the game.
In Gen IV, Gligar evolves into Gliscor when leveling up at night while holding a Razor Fang. Like with Sneasel and Weavile, it’s probably likely that Pokémon GO will opt for a simple 50 Candy evolution instead, though a Razor Fang may be necessary to attain from a PokéStop.
Swinub and Piloswine
The Swinub line gets a new evolution in Gen IV, with Piloswine evolving into Mamoswine if leveled up while knowing Ancientpower. Like other previously discussed move-specific evolutions, it’s likely that Pokémon GO will just require Candies for evolution, and Mamoswine will probably necessitate 100 Swinub Candies specifically.
Porygon and Porygon2
Porygon needed the Up-Grade item to evolve into Porygon2 when Gen II was introduced into Pokémon GO, so it’s likely that Porygon2 will need a Dubious Disc to evolve into Porygon-Z once Gen IV is introduced. It will also probably need 100 Porygon Candies.
Ralts and Kirlia
Here we have the first split evolution line of Gen IV. Similar to how Gloom needs 100 Oddish Candies to evolve into Vileplume or both 100 Candies and a Sun Stone to evolve into Bellossom, it’s likely that Kirlia will need 100 Ralts Candies as well as a Dawn Stone to evolve into Gallade, while still needing just 100 Candies to evolve into Gardevoir. It’s also possible that only male Kirlias will be able to evolve into Gallade, as is the case in the mainline games.
Nosepass is another Pokémon that will only evolve in certain locations in the mainline games. In Pokémon GO, you’ll probably just need 50 Nosepass Candies to evolve it into Probopass.
Duskull and Dusclops
The Gen IV evolution in the Duskull line, Dusclops, is another one that requires an item in the mainline games. Pokémon GO will very likely require 100 Duskull Candies for evolution, and possibly require the Reaper Cloth item, which would be attainable from PokéStops.
Snorunt also has a split evolution line in Gen IV, so it’s likely that it will need 50 Snorunt Candies along with a Dawn Stone to evolve into Froslass. In the mainline games, only female Snorunts can evolve into Froslass, so that may be a factor in Pokémon GO as well.
Along with the previously mentioned Budew, Gen IV introduces a ton more baby Pokémon which will very likely only be attainable by hatching Eggs. Due to this, it will probably behoove you to stock up on as many Egg Incubators as you can. New baby Pokémon in Gen IV include Budew (evolves into Roselia), Chingling (evolves into Chimecho), Bonsly (evolves into Sudowoodo), Mime Jr. (evolves into Mr. Mime), Happiny (evolves into Chansey), Munchlax (evolves into Snorlax), Riolu (evolves into Lucario) and Mantyke (evolves into Mantine).