What is the Sinnoh Challenge?
Inside your binocular menu, you can find the information about this challenge. Pokemon Go wants you to collect 9 new Pokemon while they are spawning more often for this timeframe. If you have previously collected this Pokemon, you can see which ones they are, otherwise they appear as black outlines. You will still need to capture these Pokemon even if you have already collected it.
If you collect them all, you will receive x3000 stardust, 15 ultra balls and a magnetic lure module. You will also get a badge and completing the challenge will count towards your Elite Collector Metal. The badge that you receive will have a number on it, showing what place you received before other trainers.
What are the new Pokemon?
The Pokemon in this set are Turtqig, Chimchar, Piplup, Cranidos, Shieldon, Combee, Buizel, Shadow Snover, and Shadow Stunky.
You can also find the following Pokemon appearing in the world: Bidoof Drifloon Glameow, Purugly and Hippopotas.
How do I catch the Shadow Pokemon?
These two shadow Pokemon, Snover and Stunky, can only be captured after defeating Team Rocket. You can find Team Rocket on PokeStops that look corrupted or through hot air balloons that are appearing in the sky. These hot air balloons can be black with the team rocket logo or meowth-themed. The Meowth-themed balloons are specific for the event, containing Jess and James to battle, back to back.
For Shadow Stunky, you will want to look for a Dark-type Team Rocket Grunt to battle against who is female and says “Where there is light, there is also a shadow”. That grunt will be the one that has the Stunky, but you might also get other Pokemon from her.
For Shadow Snover you will need to find an Ice-type Team Rocket Grunt, who will say “You’re gonna be frozen in your tracks.”
What about the other Pokemon?
Unlike the last event, many of these pokemon are actually exclusive, with Shieldon, for example, appearing through hatching a five-kilometre egg. You will need to find these eggs by spinning PokeStops and hoping for an egg that has a Shieldon. You will not know what’s in the egg before it hatches, so fingers crossed!
Many of the others you will see in the world, but do continue hatching some eggs.