Okay, well I'm just about stumped. Only thing I have is the Squiddy from Phantom Hourglass and Spirit Tracks. They're those little flying jellyfish things in the sea and the Ocean Realm that give you money when shot.
Logic being, well, they die if you just ignore them ("interesting way of killing me"), but if you don't see one you can't get any money from it because it will just die. I guess if you spend too much time shooting one, something else might kill you... And they're in the ocean...?