While not new to the series, these non-Pokemon assist characters were updated for the new Super Smash Bros. Ultimate.
Some old characters don't make the return while some others do.
Some are weak.
While others can be quite powerful. Either in sheer brute force.
Or some magical trickery.
Since it's practically impossible to fit every video game character of merit into the game, some can only see glory as trophies. I'm glad to see Springman from Arms, which I felt was a very underrated game from Nintendo. Waluigi is still a trophy, which may have killed the dreams of fans who wanted to see him as a real playable character.
Like the pokeballs, they're one of the best items in the game.