DeNA has announced that the Ghost and Poison-Type Egg Event will take place from October 24th, 2021 at 11:00 p.m. until November 7th, 2021 at 10:59 p.m. in Pokémon Masters EX. The Pokémon Hatchable from Eggs During This Event include: Gastly, Ekans, Koffing, and Grimer.

Ghost and Poison-Type Egg Event

Ghost and Poison-Type Egg Event under way! Hatch Ghost-type and Poison-type Eggs! You can check out the Ghost- and Poison-Type Egg Event during the time period below. In this event, you can receive an Egg from Professor Bellis that hatches into a Pokémon that is either Ghost type or Poison type!
Note: During this event period, you cannot receive Eggs from Professor Bellis by completing areas outside of this event.

Pokémon Hatchable from Eggs During This Event

• Gastly*
• Ekans*
• Koffing
• Grimer

Note: Pokémon listed with an * may hatch as Shiny Pokémon.

Limited-Time Incubator

One limited-time incubator will be added to Bellis’s Lab for the duration of this event only. Try hatching lots of Eggs during the event period!
Note: If an Egg is still in the limited-time incubator when the event ends, the limited-time incubator will remain active until that Egg hatches.

Lineup Bonuses

You have an increased chance of receiving Eggs if you take on event battles using teams that feature specific sync pairs. The more of these sync pairs you place in your lineup, the higher your Egg reward rate will be!

Applicable Sync Pairs

• Player Character Sync Pairs Egg reward rate: ×1.4!
• Ghost-type and Poison-type Player Character sync pairs Egg reward rate: ×1.8!
• Ghost-type and Poison-type sync pairs Egg reward rate: ×1.2!

The lineup bonus is ×1 by default and varies according to which sync pairs are on the team.
Example: If you place a ×1.8, a ×1.2, and a ×1.2 sync pair on your team, your chances of receiving an Egg will be increased by ×2.2.

Event Missions

You can take on special missions during the event period. Check the Missions screen to learn more!

Date/Time

October 24, 2021 at 11:00 p.m. - November 7, 2021 at 10:59 p.m.

Important

• To participate, you must have completed Main Story Chapter 1: The More the Merrier (Normal) in single-player.
• The sync pairs that appear as opponents in battle have different capabilities than those you can actually obtain.
• All mission completion rewards must be claimed within three days of the mission period ending.
• The time period and featured content are subject to change without notice.

Source: https://pokemonmasters-game.com/en-US/announcements/Event_3090_4W_5