How do you beat doorguy the third in paper Mario?

there is a glitch in the game and in most games. When you come up to the bit where you have to defeat doomba, hover your mouse in the game screen the right click and find the tabs that says "play" and underneath "loop" hit the play tab and that will defeat doomba and take you to the next bit. xD It takes the fun out of it though good tip.