Koopa The Quick

Koopa the Quick is the major alternative boss of most slide levels. They will race you to the bottom of the slide, and presents a star when defeated.

Princess' Secret Slide
Works as listed above.

Super Secret Slide
Works as listed above. This alternative boss fight is considered non-canon.

Pokey Oasis
Works as listed above. This alternative boss fight is considered non-canon.

Mario Riding Through The Slippery Slide
Works as listed above. This alternative boss fight is considered non-canon.

Mario's Dream
Works as listed above. This alternative boss fight is considered non-canon.

Trivia

 * One of the few alternative bosses that are regular enemies in the main game.