Really this is something the game should have been doing for months but better late than never! From the 26th of October to the 1st of November, the folks behind the game have confirmed that you'll be seeing more spooky Pokemon around. Which includes Drowzee's for some reason - mostly I just find them annoying, not scary.
There are also big candy incentives to getting out to play, just like real Halloween! Every new Pokemon caught comes with double the amount of candy, and you'll get two pieces for every little creature you transfer to Professor Willow.
Another big change is the fact that walking around with a Buddy Pokemon is going to give you four times as much candy. That's a huge difference, making this the perfect time to get closer to evolving that Magicarp!
Niantic has also dropped a new update which colour codes eggs depending on how long it takes to hatch them and also added types to the Pokemon info screens. Get the latest update now and get out collecting candy from the 26th of October.