As reported by @Wipeoutjack7, the upcoming new entry in the Mario sports series features a total of 20 character slots. As the game will only feature 10 characters at launch, it is likely the 10 additional slots will be used for characters that will be made available after launch via the already confirmed post-launch free DLC.

— Jack (@Wipeoutjack7) May 27, 2022 Mario Strikers Battle League launches on Nintendo Switch on June 10th worldwide.

Join an online club to push and shove your way up the ranks - Band together with up to 20 strikers online and compete against other clubs for points. Find the right club for you, team up with friends, and bring your own striker style to the table. Strive to become the world’s top club each season! Pummel the pitch with up to 8 players - 8 players can go for the goal on one Nintendo Switch system, with local wireless, or online. Bring along a secondary striker on the same system in online battles, too. Locally, 4 players on each team can go cleat-to-cleat in individual matches. Mario Strikers Battle League May Get at Least 10 Characters After Launch - 1Mario Strikers Battle League May Get at Least 10 Characters After Launch - 68Mario Strikers Battle League May Get at Least 10 Characters After Launch - 77Mario Strikers Battle League May Get at Least 10 Characters After Launch - 29