DeNA has announced that the Champion Stadium: Johto Challenge is under way from September 5th, 2021 at 11:00 p.m. until October 10, 2021 at 10:59 p.m. in Pokémon Masters EX.

Champion Stadium: Johto Challenge under way!

Champion Stadium Under Way! You can check out the Champion Stadium: Johto Challenge during the time period below. Defeat powerful opponents for a chance to enter the Hall of Fame!

Johto Challenge

Johto Challenge Date/Time

September 5, 2021 at 11:00 p.m. - October 10, 2021 at 10:59 p.m.

Important

• You can participate in the Champion Stadium after you complete Main Story Chapter 10: A Reason to Battle (Normal) in single-player and collect all PML Badges.
• Medal acquisition and Hall of Fame information will be saved for each region regardless of event date/time.
• Details about the time period and featured region will be included in notifications going forward.
• The time period and featured content are subject to change without notice.

Source: https://pokemonmasters-game.com/en-US/announcements/Event_3080_1W_1