If it's been some time since you caught a Pikachu or joined the hunt for a Dragonite, the Halloween update for Pokémon Go should lure you back into the game.
From Oct 26 to Nov 1, celebrate Halloween Pokémon-style: There will be more sightings of Gengar, Haunter, Gastly, Hypno and Drowzee, so your Pokédex should see an increase. You'll also see more Golbat and Zubat flying about, but ignore those common bats and toss your Poké Balls at the elusive Gengar.
There's also a two-fold increase in candy (six candies instead of three when you catch a Pokémon; two candies instead of one when you transfer a Pokémon). Have fun trick-or-treating!
And if you stuck around long enough to get the Buddy feature, the Halloween update means whichever buddy Pokémon you select will earn four times as many candies. Good news if you have a Magikarp for a buddy: you usually need to walk with it for 1km to get one candy, but you only need to walk 0.25km now to get the candy. You'll get a Gyarados in no time.
Still need clarification? Watch this video:
Not keen on walking about town on Halloween catching Gengar? Here are the best things to do this Halloween weekend.