Masahiro Sakurai has introduced a new gameplay element called Spirits in Super Smash Bros. Ultimate.
To replace character trophies which take too long to develop, Nintendo came up with Spirits, which are based on video game characters outside of the playable fighters. Spirits can be used to power up fighters in the game, and you can acquire spirits by winning in Spirit Battles.
There are many types of Spirits, and you can use them to power up amiibo, send them to the real world for their cores, and much more.