This game has some awesome bosses. Special mention to Red-Brief J, Dino-Mighty, Clown-a-Round, Dual Dragon, and... hell, all of them.
Wario proves his Badass status by pummeling the final boss Obviously Evil Black Jewel so much it sheds tears before exploding. "I WIN! I WIN! HAHAHAHAHAHAAA!" For extra awesome, collect all the Spritelings and retrieve all of Wario's treasure to see his castle restored to its former glory in the ending.