Prepare for a ghastly good time during Pokémon GO Halloween 2019!
Activity 1 - Starts: Thursday, October 17, 2019, at 1 p.m. PDT (GMT −7)
Rescue more Shadow Pokémon from Team GO Rocket — Be ready to rescue the following Pokémon at PokéStops near you: Weedle, Kakuna, Beedrill, Electabuzz, Magmar, Lapras, Mareep, Seedot, Nuzleaf, Sableye, Trapinch, Cacnea, Shuppet, and Duskull.
New avatar items like: Zubat Bag, a Pikachu Onesie, a Cubone Cap, a Litwick Cap, and a Mimikyu Bag.
If you’re lucky, you might encounter Shiny Yamask.
Activity 2 - Starts: Thursday, October 17, 2019, at 1 p.m. PDT (GMT −7) to Friday, November 1, 2019, at 1 p.m. PDT (GMT −7)
More Ghost- and Dark-type Pokémon will be appearing in the wild, in Eggs, and in raids — Gastly, Murkrow, and more will be appearing. Making its Halloween debut is Yamask.
Pokémon wearing creepy-cute Halloween costumes arrive in raids and in the wild! — Look forward to Bulbasaur wearing Shedinja costumes, Charmander wearing Cubone costumes, and Squirtle wearing Yamask costumes in raids. In the wild, be on the lookout for Pikachu wearing Mimikyu costumes! If you’re lucky, you might even encounter these alarmingly adorable Pokémon as Shiny Pokémon!
The Pitch-Black Pokémon makes its ominous debut in Pokémon GO! Darkrai will be appearing in five-star raids.
Frightful and fun Field Research tasks will be available for a limited time during this event.
You’ve received a spooky message. Check out your Special Research when the Halloween event begins, Trainer, and you might face a Forbidden Pokémon…
Information Source: https://pokemongo.nianticlabs.com/en/post/halloween2019/