How do I defeat the Mouse and the other beast in the Stagnant Swamp?
Please help me, I'm stuck.

You don't defeat the mouse; all you can do is run away from it. You can jump on it as much as you want and it won't die.

Which other beast do you mean? The ghost or the bug?

euhm actually I mean the beast that sits in the water waiting when you are on a turtle and you have to jump onto the thing to climb and then the beast comes out of the water. But you can tell me about both.

P.S.: sorry for my bad English, I'm not used to write or to speak english.

Don't worry about your English; you're fine. =)

You know how you can slide down ladders by pressing B and Down? That's what you have to do to the bug. But make sure you don't touch its head, or you'll fall off the ladder and most likely into the water.

As for the ghost, just turn on all the lights in the room. This one's a bit more challenging.

Hope that helped.