Super Princess Peach

Well, if you can hit him, and he won't die, it's probably because you have to hit him a lot of times to kill him. It even says so in the game.

You have to hit him three times, once on each level he appears on.

He first appears on level 2-5, on the second screen. Keep entering and exiting the pipe until you see him swimming in the water. Follow him closely and either jump on him or whack him with your umbrella as soon as you see him jump out of the water. You'll know you hit him if he starts blinking. If you missed him, enter and exit the pipe until he appears again.

He next appears on level 5-5, on the very last screen (one with the goal post). Enter and exit the pipe here until he appears. He'll be sleeping on the sand near the pipe when he does appear. Use the walk button to creep up on him and give him a whack. If you miss, do some more piping till he appears again.

Finally, he'll show up on 6-4, once again on the very last screen (with the goal post). He'll be directly above you as soon as you enter this room. If you see him, IMMEDIATELY hit your cry emotion heart, run up the hill, and then run to where he is and jump on him. If you miss or you're too slow, you know the drill.

Congratulations, he's dead. All it does is add him to your Glossary.