That One Boss: Kracko in Extra Game. He moves very fast, giving you next to no time to react. Instead of throwing Waddle Doos, he now throws bombs. This boss battle is more about luck than anything else.
Though there is a way to make him the easiest boss in the game. If you stand in the left corner, you only have to worry about him charging at you and inhaling his bombs. The beam attack cannot hit you.
Kabula's shots spiral erratically, making it hard to dodge them, to the point that fights with her can easily just turn into a battle of attrition (especially in Extra Game).