How do you beat pluck the parana flower in super Mario 64 Ds?

If you mean "Pluck Piranha" from Tiny Huge Island, I suggest you do what was dome in the original SM64-- Jump around the outside of the wall of the fortress until you get to the pipe at the end. You have to be big in order to get across, I guess... You already know you can't fall in the water or you're pretty much screwed, but other than that, if you're big, enter the pipe at the end of the way to shrink yourself down, then destroy the Piranha Plants that surround you. If I'm correct, the star should hover over where the right Piranha Plant dropped the star.