The Mermaid Princess

Ok so u've probably beat tha game by now but just in case u didnt or for other u havnt... to beat the mermaid u need to hit her twice then move out of the way.if u look and listen to the music carefully u can tell where she will drop and wen she is going to throw up. i know its hard bt keep tryin.it took me about 15 tries bt if doable.the easiest weapon is the pipe because it has a better range of motion.

Ok, just did this in 10 mins after wasting the whole of yesterday.. Here's my tips:
Use the cleaver, her attack collision detection is ropey, if you swipe continuously at her you'll find her swipe attacks seem to miss.

Getting behind her is unneccesarry, the side is enough, just keep swiping and leg it if you get two hits (she'll usually retreat anyway but that vomit attack is lethal, so don't risk it after the two hits)

If she vomits and you get stuck in it, don't move... Moving in vomit hurts, standing in it until it goes less so.

Only attack her if she's neerby and in the open half of the room, you've got all day, so take the easy chances, and leave her to vomit away when you're far away.

Make sure you stand in the corner of the open half of the room seeing as much of the room as possible, so you can see where she comes down, if her shout is loud, run, she's probably coming down above you

Search for powerups before the battle, select candy/shortbread and select find... Try in loads of areas, there's a lot of candy hidden around the ship.

I see Feb 17 2010 is when you asked this question (2 years ago) so I'm guessing you've figured out how to beat the mermaid princess and probably beaten the game as well. Just for kicks, I'll answer you though.
To beat the mermaid princess, you need a long-range weapon. The pipe is pretty good. (I'd personally use the syringe or umbrella. Lol. But those weapons are only available if you have beaten the game once)
After you have your weapon, hit the mermaid about
27 to 30x.