Challenge

Challenge mode is a new feature which will be included in Sizzle Season 2023. Officially a replacement for League Battle from, Challenges are focused around special modes with unique in-match conditions. They can be played solo or with a team, and feature a two-hour ranked play window similar to League Battle, but unlike League Battle's constant rotations, the windows only occur at a few specific times during a season.

Previewed
Three types of Challenges with unique conditions were revealed as part of the Sizzle Season 2023 announcement: "Too Many Trizookas!", "Foggy Notion", and "Extreme Jump Battle".

The @SplatoonJP Twitter account also confirmed that the monthly event battles (ツキイチ・イベントマッチ in Japanese) that appeared in 's League Battle mode will return as Challenges.

Quotes
"Ballistics aside, we have an update about the League Battle feature from Splatoon 2. A similar feature is coming in Sizzle Season with a new name - Challenges! These are an exciting new way to battle with special rules for a limited time, and you can join solo or with friends."

- @SplatoonNA on Twitter

"A new mode - Challenge - is coming to #Splatoon3 in Sizzle Season 2023!

Look forward to monthly challenges and events with special rules. Test your Turf War talent on a brand new stage in the first event, taking place 03/06!"

- @NintendoEurope on Twitter