You can build your very own Super Smash Bros. Ultimate Mii character to also unlock the Mii Brawler, Mii Gunner, and Mii Swordfighter. Or earn them. Set the red and blue torches in the World of Dark to a 4:40 clock for the Mii Brawler. Duck down to the Island area in World of Light for the Mii Gunner. After, head to the Town area for the Mii Swordfighter.
Match a fighter with a primary spirit from the same game franchise for a 20% damage buff! Just pair the same symbols in the bottom left of the screen. This leads to combos like Mario and Bullet Bill. Pikachu and Groudon. Solid Snake plus Otacon. And Richter Belmont with Alucard.
There’s a secret “true” ending for World of Light. Defeat Master Hand and the Dark Spirits. Then beat Crazy Hand and the Light Spirits. Once both hands are freed, balance beating the same amount of Dark Spirits and Light Spirits. This will keep the small bridge at the top of the stage in the centre. Follow that bridge up for the true ending.