At the tail-end of Kirby's Return to Dream Land Deluxe's True Arena, he gains a significantly more powerful and dangerous moveset, bringing him up-to-speed with later "Soul" bosses like Soul of Sectonia, Star Dream Soul OS, Void, and Chaos Elfilis. During the battle, after he takes enough damage, he will also lose his white oval eyes, leaving only the single red eye inside his mouth.
