Alongside the release of the game
To promote the release of Square Enix's Trials of Mana on the Nintendo Switch this week, Super Smash Bros. Ultimate
It lasts a total of five days and begins this Friday on April 24 (the same day as the Trial of Mana's release) Defeating each one in battle will earn you more SP than usual.
We'll update this post with more information soon.
(source japanesenintendo.com)