From Friday, July 28th 2023 to Sunday, July 30th, 2023 at 23:59 UTC, then again from Friday, August 4th, 2023, to Sunday, August 6th, 2023 at 23:59 UTC, Rillaboom with the Mightiest Mark will be appearing in 7-star Tera Raid Battles at black crystals in Pokémon Scarlet and Violet.

Prepare to Face a Mighty Rillaboom!

Catch a Rillaboom with the Mightiest Mark! Rillaboom with the Mightiest Mark will be appearing in 7-star Tera Raid Battles at black crystals from Friday, 28 July 2023, at 00:00 UTC to Sunday, 30 July 2023, at 23:59 UTC, then again from Friday, 4 August 2023, at 00:00 UTC to Sunday, 6 August 2023, at 23:59 UTC.

Rillaboom cannot normally be encountered in Paldea, and the Rillaboom appearing during this event has Normal as its Tera Type. Be prepared—this Pokémon is a formidable foe, and it’s got the Mightiest Mark to prove it! Work together with your friends to topple this powerful Tera Pokémon!

This special Rillaboom can be caught only once per save data. You can still participate in Tera Raid Battles against this Rillaboom to obtain other rewards if you’ve already caught it.

This Rillaboom may be featured in future events or become obtainable through other methods.

Event Schedule

Friday, July 28th, 2023, at 00:00 UTC to Sunday, July 30th, 2023, at 23:59 UTC
Friday, August 4th, 2023, at 00:00 UTC to Sunday, August 6th, 2023, at 23:59 UTC

Featured Pokémon

7-star Tera Raid Battles: Rillaboom with the Mightiest Mark

What Is a Tera Raid Battle?

In a Tera Raid Battle, you’ll work together with three other Trainers to defeat a powerful Tera Pokémon before time runs out. The kinds of Pokémon encountered during Tera Raid Battle events will vary. Pokémon encountered in Tera Raid Battles may have a rare Tera Type.

Information about Tera Raid Battle Events

• To participate in Tera Raid Battle events, please download the latest Poké Portal News by selecting Poké Portal from the X menu, then Mystery Gift, then Check Poké Portal News. You do not need a paid Nintendo Switch Online membership to receive the latest Poké Portal News.
• After completing certain postgame events, you’ll be able to find black Tera Raid crystals. However, players who haven’t completed these events may still participate in these Tera Raid Battles by joining other Trainers in multiplayer.
• A paid Nintendo Switch Online membership (sold separately) is required to participate in Tera Raid Battles with other Trainers online. Terms apply.

Source: https://sv-news.pokemon.co.jp/en/page/71.html