For three days starting on Friday, January 29th, 2021, the
Full of Energy! Yellow Spirits (元気いっぱい! 黄色いスピリッツ) event will be held in Super Smash Bros Ultimate for the Nintendo Switch! During this period, many yellow characters will appear on the Spirits Board and if you win a battle, you will earn more gold than usual. Pikachu and Tapu Koko will be two of those Spirits.
Source:
https://twitter.com/SmashBrosJP/status/1354232660567093249