This topic should have gone under "game help."
I assume that you can get to part 2 of the battle, right? If not, then you have no hope. Part 1 is ridiculously easy.
Anywho, the biggest obstacle in part 2 (the "Cackletta" battle) is the very beginning, when both Mario and Luigi start off with only 1 hp. YOU MUST NOT GET HIT BY CACKLETTA'S FIRST ATTACK. Practice, practice practice, and you should be able to avoid her attacks eventually. She only has a few in the beginning...I think the worst one is the one where she swings her arms around in circle which you have to either jump over or duck under.
Anywho, once you can get past her first attack, the rest of the battle isn't that hard. Use a super nut to heal both Mario and Luigi, then attack in this order: arms first, then head, then chest. When the chest is open, bust out your bros attacks like there ain't no tommorrow. Unless you're REALLY desperate, do not heal until the chest has closed again. When the chest DOES close, use a super nut if you need to, then start the cycle over again: arms, head, chest.
Toward the end of the battle, Cackletta will bust out some new moves, including an annoying move in which she fires two separate lazers from her eyes at Mario and Luigi. Watch the eyes, and jump (if you need to) when the timing is right...BEFORE everything freezes. You can't do anything at all for the one second time period when everything is frozen, but Cackletta won't do anything either (her eyes will not change direction), so the pause is really only included to distract you and throw off your timing for future lazer attacks.
One thing to watch out for is if the head uses the "attack up" move on one of the arms. If this happens, then that one arm's individual attacks may temporarily be powerful enough to kill you in one hit. If this is the case, and you are not confident that you will be able to avoid all of that arm's individual attacks, then you should probably attack that arm first to destroy it (unless the chest is open!).
Anyway, these tips are in no way comprehensive, and if you really want help, you should probably look for a walkthrough on the net (gamefaqs.com has some great walkthroughs). If all else fails, just play better!
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