Nature and abilities
The Crystal King is invisible, save for his robe, crown and floating yellow eyes. He can disappear and reappear altogether in a flurry of snowflakes.
The Crystal King is exceptionally powerful. He can levitate, summon Crystal Bits to use as ammunition and shoot freezing beams. In desperation, the King can make fake clones of himself and recover his HP; if not beaten quickly enough, the Crystal King will recover 20 HP at least three times, and he and his army of illusory copies will unleash a powerful blizzard attack. There is no way to tell the Crystal King apart from his clones, leaving Mario to guess or use an attack that hits all enemies.
When Mario defeats him, Crystal King says, "Oh no! The last Star Spirit!! King Bowser, forgive meeeeeeeee!!" before spinning and disappearing in a flurry of sparks.
Like the other bosses, Crystal King appears in the parade at the end during the credits. Two Duplighosts are impersonating him. The real Crystal King removes their disguises, but is carried away by his Crystal Bits, seemingly to his surprise and against his will.
The Crystal King also makes an appearance in volume 27 of Super Mario-Kun. Before the fight, the Crystal King announces his presence using Ice Bolt by freezing Kooper. The Crystal King borrows his attacks from the original game such as hurling Crystal Bits and creating duplicates of himself. After an assortment of attacks, including Mario's using smelly clothing, Kooper uses a flaming shell to defeat the Crystal King.